"Where in the Bible does it say that God doesn't have forms?" It doesn't, of course. This comes from Greek philosophy.
It is excused by the pretense that John 4:24 "God is a Spirit..." means that God is a formless blob. But in reality, such an argument fails miserably, due to Matthew 14:26 "And when the disciples saw him walking on the sea, they were troubled, saying, It is a spirit; and they cried out for fear."
From there we see that a spirit may have form. Obviously when the disciples saw Jesus walking on the water they did not see a formless blob, but the form of a man walking on the water. Yet the said "It is a spirit," showing that the phrase "God is a Spirit" is not a proof that God is formless.
The Bible clearly says that Jesus sits at the Father's right hand (Mark 16:19, Acts 7:56 where Stephen describes it as something he actually saw, and many other passages), and Jesus is intended to be understood as still corporeal, having been bodily raised from the dead (thus, implying an actual seat). This implies that the Father has human form, despite being non-material and a spirit, and it is almost atheistic to buy into the vain philosophy (Colossians 2:8) that says God is formless. People need to quit covering for this antichristian philosophy with a misuse of John 4:24. There is an insistence on scandalizing people with this "God has no form" and pushing it for no other reason than to harm people's faith and create agnosticism, and its sickening.
To the argument in another answer which says that passages which say God has not been seen (1 John 4:12, John 1:18) and one which says he cannot be seen (1 Timothy 6:16) imply formlessness, I would answer with the actual text of 1 Timothy 6:16
Who only hath immortality, dwelling in the light which no man can approach unto; whom no man hath seen, nor can see: to whom be honour and power everlasting. Amen.
Its not formlessness that's being spoken of, but that the light in which he dwells is so bright we wouldn't be able to see in it.