If the barrels are of any value, send them to someone with a Sunnen setup. I believe there are a number of barrel guys who do. I have heard fine reports and seen the work from Allems and I would not have a problem going to them. Anybody else you gotta ask somebody else.
If the barrel isn't particularly valuable, personally I'd just spin a wire brush thru it to get the corrosion out and shoot it. Pits won't mean squat to a shotgun barrel in performance terms and if you kept it clean it won't get any worse.
I mean, it's a shotgun. Right?
Dr.WtS