Tisk tisk, getting a fish without proper housing! I would suggest placing an add in the paper, and call several lfs's to see if anyone will take it. Or, better yet get your fishy a bigger tank.
Edit, just re read your post. The fish too big for the tank was just an example. Sorry for snapping. I'm tired But as I said, it does depend on the lfs
Just call and ask your lfs. My lfs will take just about anything (that's healthy that is) and he gives you credit. For some reason my dad had a cichlid in his swordie/mollie tank, and I took him to my lfs and I got a trio of swordies for him.
Usually a good LFS will take the fish and give you a discount on your next purchase, but as I have heard, some won't take fish. It's best to avoid those and keep searching