According to Stephen Runciman's The Great Church in Captivity (excerpt), the Orthodox Patriarch Jeremias II wrote a letter detailing the differences between the Orthodox doctrines and Lutheran teachings; is an English translation of the letter publicly available, and where can I find it? My searches keep taking me back to the linked excerpt above.
If you are talking about finding it online, you aren't going to have any luck. These letters, as far as I know, are not available to read online.
However, if you are willing to spend some money, an English book compilation of the letters by George Mastrantonis can be bought from Amazon (published by Holy Cross Orthodox Press, however it seems to be more expensive on their website).
Quoting a review on Amazon by Dusk:
I hope this helps! Have fun...