My answer is hardly based upon poor database, wild speculations and extrapolations. If you have access to any of the data I claim to have no access or any other useful data or suggestions for extrapolations, please write a comment.
What is a canon lawyer?
I am not sure what kind of persons you mean when you say "canon lawyer". According to Wikipedia the word "lawyer" is inconsistently used in the English speaking world. As I am from Germany I have no idea in which way the term "canon lawyer" is used. One of your sources and EWTN use the term for someone who has an license in canon law (academic degree). In this answer I will do the same and use the terms "canon lawyer" and "canonist" in a synonymous way.
How many of them are there?
Ask the universities
To find out how many canon lawyers exist means to find out how many people got a license in coanon law. The universities know how many graduate with this degree. I searched on the websites of the Catholic University of America in Washington, D.C, the Papal University Gregoriana in Rome, the Ludwig-Maximilian-Universität in Munich and the Westfälische Wilhelms-Universität in Münster. The only information I found was a list of all license theses since 1990 in Münster and statistics of all degrees in 1998-2003 in Munich. Acoording to these sources they gave about 7 licenses per year in Münster and no licenses at all in these years in Munich. I believe Munich was in an extraordninary situation in these years and an average of ca. 7 students per year seems to me a minimum for regular teaching for a faculty.
Who else could know figures?
The Congregation for Catholic Education (for Educational Institutions) ist the Vatican supervisory authority for the universities and could know the the figures for every university and the whole world. Unfortunately, I found no such figures on their website. I suspect such numbers can be found in the Annuarium Statistica Ecclesiae (statistical yearbook), but I do not have access to it.
We know there are 43 faculties and institutes, 48 if we count outpots, which award the licenciate. If we assume there would be at least 7 graduations per year and the canonists work at least 30 years in this field, we have at least 48*7*30 = 10,080 active canon lawyers worldwide. For at most 50 students per year (only my gut feeling) we would have 48*50*30 = 72,000.
As it is asked explicitly for the US: The only faculty of canon law is at the Catholic University of America. So there may be between 1*7*30=210 and 1*50*30=1,500 active canon lawyers in the US.
As we have no total figures we have no data about distribution. But I assume that density of canonists correlates with densitiy of faculties and institutes of canon law. We see in the maps of faculties and institutes, that they are not uniformly distributed in the (catholic) world. In countries without such an institution there wont be many canon lawyers, only the ones who study abroad at next faculty or in Rome (there are 8 faculties of canaon law in Rome). In Europe there are many faculties and institutes, in every bigger catholic country at least one. In the rest of the world there are only a few institutions. In North America may be the best situation out of Europe, because there is a faculty in each of the three countries.
Are they enogh?
For the whole world the Congregation for Catholic Education (for Educational Institutions) says: No. In April 2018 the congregation released a new instruction "The Study of Canon Law in light of the Reform of the Matrimonial Process". Apart of new norms for the universities the instruction complains about the situation of the jurisprudence and teaching. Because of the need it even calls for new courses below the level of licenciate for a part of the staff of the courts.
There is a general decline in the number of students, such that in some situations a balanced academic life cannot be ensured.
Having Tribunals staffed by those who are competent and well-prepared is not a luxury. The good of souls demands a solid formation, which is the main task of academic institutions.
To meet the urgent need for a greater number of clerics, lay men and women, and religious who are well formed in canon law, even though they do not (yet) possess the degree of Licentiate or Doctorate, so as to make up for the lack of competent personnel in many dioceses around the world, some possible formation courses are proposed.
So we see, there is need of good educated canonists. We may assume that the biggest need is where only few faculties are. I have no idea about the situation in the US.
More speculative figures, please!
How many canon lawyers do the world and the US need? Let's make a extrapolation again. I assume based on my experiences that there are enough but not way too many canonists in Germany. So we have 2 canon law institutes in Germany for 23,300,000 Catholics according to the German bishops' conference in 2018. Worlwide there are 1,285,000,000 Catholics according to the Vatican for 2015. So we would need 1,285,000,000/23,300,000 * 2 = 110.3 institutions. We only have 48. So we would need to double the number of canonists. As this number is very speculative, I believe the more important problem is the distribution of the canon lawyers over the world.
Same calculation for the US with (officially) 68,500,000 Catholics in 2017 according to the Center for applied research in the apostolate: 68,500,000/23,300,000 * 2 = 5.9 faculties. There is only one. I do not know whether their is really a lack of canonists in the US or the whether the Catholic University of America just has more students of canon law than the institutions in Germany.
Based on public avavible internet sources it is very hard to find any exact number of canon lawyers or needs for them. The first may be easier with the printed yearbooks of the universities and the Vatican. The latter has to remain speculation (but maybe based on better database). The only thing we know for sure is: The Vatican thinks the church needs more well educated canonists.