Where do I get silencer barrels for my pistols?
Who makes the best suppressors?
Lonewolf, Jarvis, EFK all make extended + threaded barrels. Google them for specifics. Jarvis and EFK could possibly take months if the barrel you're looking for is not in stock. I wont even consider BarSto, as they will take months and lie to you along the way saying "2 more weeks" ad nauseum.
Your second question is like asking "who makes the best car", or "who makes the best hard drive", its a loaded question and will net you all manner of answers. Even companies I think of as "good" tend to have a crappy can or two in their line up.
Then there's the question of what caliber/gun to silence? 22 and 9mm work great, 45 sounds terrible (in my not so humble opinion).
If I was buying now, I'd go with SWR for 9 and 22 pistol cans, AAC for 223 and 308 rifle cans.
There a few well-known manufacturers that have huge reputations built on glossy advertising, fluff and past performance but now have poor designs or made demonstratively false claims about their products. I'd avoid those.
If at all possible, go hear as many different silencers as possible before buying. There's a decent size community of oregon silencer owners that congregate on ar15.com's home town forum.
-T