IM not sure about on the lake but there used to be a place in auburn just a couple of blocks off campus. Sorry I can't remember the name and haven't been that way in forever but it was a one established business so hopefully they are still there.
A personal friend of mine is a NAUI instructor. He taught my wife and I, and many of our friends. He is really good and very safety focused. He's not in the immediate Lake Martin area, but visits frequently and has all the equipment for training and could do some classes remotely as well as at the lake. He is also used to doing check-out dives on inland lakes as we did one on lake Allatoona years ago and also visited the rock quarry there in AL.
I highly recommend him, besides the fact that he is a friend, mainly because of his focus on safety. Let me know if you would like his contact information.