Truly handicapped people get trained through specially trained instructors, and they don't have standard certifications.
I suggest you rethink this. You will be amazed what a good swim instructor can do for you. A number of years ago I watched a student do the swimming requirement beautifully--she looked like a real expert swimmer. I then learned that only a few months before she had done a discover scuba class in Australia and almost drowned. She was a non-swimmer who had struggled to learn on her own in the past. She thought she was OK enough for scuba, though, so she tried the Discover Scuba class, and it almost killed her. She cried all the way back to the boat, but as she cried, she resolved not to be stopped by it. Immediately upon her return to the USA, she got into a swim class. A few months later she was the star of her scuba certification class.
You really do need to be able to swim well enough to pass the required swim test. It is not that hard--it should not take too many lessons to get you there.
I don't see much value in swim instruction. I can find all the detailed stroke technique analysis I need on Youtube for free. I get the idea of the front crawl, but that whole trying to breathe with your head turned while water goes in your nose, makes it a bit difficult. Coordinating legs and arms is very hard, and most foot/leg positions seem either useless or minimally useful for propulsion, though II have learned how to kick and move backwards.
I suggest you rethink this. You will be amazed what a good swim instructor can do for you. A number of years ago I watched a student do the swimming requirement beautifully--she looked like a real expert swimmer. I then learned that only a few months before she had done a discover scuba class in Australia and almost drowned. She was a non-swimmer who had struggled to learn on her own in the past. She thought she was OK enough for scuba, though, so she tried the Discover Scuba class, and it almost killed her. She cried all the way back to the boat, but as she cried, she resolved not to be stopped by it. Immediately upon her return to the USA, she got into a swim class. A few months later she was the star of her scuba certification class.
You really do need to be able to swim well enough to pass the required swim test. It is not that hard--it should not take too many lessons to get you there.