Owning NFA items goes a little something like this:
You need to fill out this thing called a "Application for Tax Paid Transfer and Registration of a Firearm," better known as a Form 4, that's gotta be signed by the chief law enforcement officer of your county, saying that you're of good moral character and won't use whatever you're buying to knock over the corner liquor store or anything else mischevious. If the CLEO won't sign, there's other folks who can, like the District Attorney or certain judges. If they won't, then you'll have to form a corporation that'll bypass all the other required stuff, like the two passport photos, fingerprints, and the FBI background check. Anyways, provided the CLEO signs, you stuff all the paperwork and a $200 check in an envelope, send it to the BATF, who then sends it to the FBI. If everything goes as planned, in 90-120 days your dealer gets a copy of the approved form 4 with a tax stamp on it and you go pick up whatever you wanted.
(paraphrased from AR15.com)
And there's a nice list of who makes suppressors somewhere in the archives of the Firearms Accessories forum.
-Quintin