A real fish shelter,cool.
I really like the idea of aquiring animals through rescue before buying any from a breeder or petshop. Not that I am against the other sources, but I'd love if more people would consider rescuing unwanted animals too.
I would suggest you get on petfinder for the fish you wish to rehome again. They do not have a fish section, however they do list fish under reptiles. Craigslist is another good source, I posted two nice large free fish from there on MFK already. Surprised nobody went after that.
Also if you nurse sickly fish back to health, you could be charging an "adoption" fee/ aka selling them.
It'd probably be best if you didn't accept every fish, what if your tank becomes just a huge species tank for irrescent sharks?. A couple of these could easily fill up your largest tank. Plus so many are sold that you won't be able to rehome them.