Buying a new barrel, even if you could locate it, isn't a one-stop solution -- barrels aren't drop-in, they need knowledgeable fitting.
Alternately, you can try very gentle taps with a ball peen hammer to flatten the dent, and a follow-up polish and range test, but I'm not sure I'd want to stake my life on amateur work. A qualified gunsmith might be a better alternative if you insist on trying to save the damaged barrel.
But if it's your carry piece and you can't rely in it, it's no carry piece at all. Best bet is to send it to S&W for repair, and in the meantime pick up a second to cover you while the primary is at the mothership.
This is the meaning of "one is none, two is one."