Call around to your local pet stores. Some stores allow trade in - basically they take the fish that you don't want and they give you store credit for you to use for a later date. If you do not have any store in that area that will take him then put an ad in the paper and perhaps see if those stores have a posting area where you can put up a flyer. And no Jacks do not grow to accomedate the size of the tank-they will get big.

Try a local newspaper or classifieds paper, or online on craigslist or a trade posting on a forum like the one at www.cichlid-forum.com, where it shouldn't be difficult to give him away. Around here the stores will take them back for free (his stunted situation makes him worthless).

*edit - stunting is the actual term for 'growing to their environment' - the latter sounds nicer, but the former is closer to what is actually happening. If he even fits into the 10 gallon with room to move and he's actually 4 years old, then he would need to be considerably smaller then he would be raised in a proper sized tank, and hence, stunted.

It's nice that you are at least looking into your options of finding a home for him rather then just "killing" him. Please don't do that. I'm sure it shouldn't be too hard to find a home. I know my vets office has a bulletin board where you can hang signs to sell things or want things, so if you have a vet near you you might want to call and see if they do, or perhaps they can even point you in the right direction of where you can take him to donate him or something.
Again, thanks for having a heart and trying to find this fish a home. The fish didn't ask to be stuck in a 10 gallon tank, so it's really not his fault. Your son should have taken responsibility for it, especially if he knew his mom didn't like fish or fish tanks....that was kind of mean on his part. I'd make HIM do what you are trying to do. His fish, his problem. But that's just my opinion.
Good luck to you. ;o)

Send him on a journey to the porcelain gods.

Place an ad. A pet store might give you credit for a purchase, then turn around and sell the fish. Just make sure it goes to someone who knows the requirement for it, and will provide a good home. It would probably be best to charge something for it, so not just anybody calls about it.