[SovietHippie]

Probably a metal working shop. Hell if you want to make a few project guns and DIY you could go as far as getting used Milling tools(Considering they are very expensive new) and make it work for YOU. I'm not sure a gunsmith could help you real steel or airsoft. Have you checked the overseas retailers yet too to see if they have some of the parts. Though by the looks of it you are probably going to have to get a custom flash hider.

EDIT: You can get threading tools if you want to DIY but it's a difficult task(Tryed it myself) and it's not redoable which is what makes it the hardest. I had them in my Tech class at school, Not exactly sure where to buy them, but I would try to see if Princess Auto has them.