You can have one done, doesn't have to be a factory deal. One thing to realize...you cannot machine on the metal after you do it without some major pain. So if you need barrel threaded for break (just for Chad LOL!) or suppressor, do it before you have the barrel coated.
Another thing...it hardens the metal to the point if you are a shoot the throat out then have the chamber set back type of person...most smiths won't want dull their reamers on a nitrided barrel.
I've seen it have no effect on barrels and I've seen accuracy degrade on barrels. It's a crap shoot.
Don't let your ears hear what your eyes didn't see, and don't let your mouth say what your heart doesn't feel