Hello,
I’m sorry to hear about your cat.
In my experience I have never found a polyp in a cat this old.
If you would like to try to find someone local to you I would recommend that you call rescues and shelters and ask if they know of anyone who is willing to sedate your cat and look behind the soft palate. There are other vets who do this. They may not have ab endoscope like the specialist does, but, it might not be needed if they can visualize it.