answer:A nice idea for your bother, points for that. :-) Crayfish are fresh water crustaceans and Lobster are saltwater crustaceans. Check with your local pet stores, Petco, etc. and also, you can google tins of articles on keeping Crayfish and, you can even order them online. Google ” Where to buy and how to keep crayfish.” There is a reddit article I browsed, but don;t have time to post the link right now. Remember, you want to provide the right environment for them, it is cruel to neglect ANY creature, large or small. Good luck in your search!