Why would you buy one when you can catch one in pretty much any large body of water around you provided that you have a valid fishing license?
Not if you want to start small and follow most minimum size rules. Also, many states ban the taking of live gamefish. For me, I can take baitfish like perch and sunnies, but it is illegal to take game fish like trout or bass. If I want to take home a game fish, legally it has to be dead.