Charlie is well known in the (custom) muzzle loading community for making an above average barrel. I will never be a good enough shot to ultimately tell the difference between one of his barrels and those from Rice or Rayl (which cost about double by the time you get them to Canada) and I do own all of them plus one from Oregon barrel and Colerain.
If you send him an email telling him what you are after he may be able to give some advice as well (maybe - black powder is his thing).
He has been in business for a good few years now - bought out all the equipment from Goodien barrels when Jim packed it in - so at least in the muzzle loading community these barrels have a good "blood line".
His barrels are made with 12L14 steel, suitable for BP and most probably air, just don't entertain dumping smokeless down one. If you want different barrel steel I'm certain he can source it but cost would probably go up. Jason at Rice barrels will build fast twist with 4140 (chrome moly), but they start @ 300 USD.
From any of the barrel builders on the other side of the border the shipping has always came in at 40-45 bucks and there is no customs restrictions/issues either leaving the US or coming into Canada - although CBSA has dinged me for taxes about 80% of the time (usually if the value listed exceeds 200 bucks).