Rusty Wood Trading has a contact for doing really nice hot blue. I've had a few things done, including an old crusty Win 94, and all the pieces have come back looking just great.
As with anything like this the metal needs to be finish polished first. Rusty can do this for you if you're not sure. But of course the more he has to do the more it costs. The hot blue is only as good as the surface prep and finish.