There are a number of options out there, but an integrally suppressed upper is likely to be quieter than a seperate can would. The downside is that unless the suppressed barrel is at least 16" under the can, you will have to also register the lower as a SBR to be legal. John's Guns (
http://www.fullysuppressed.com/arplatform.html) is one source. I personally run an AAC can on a number of my guns...another plus of the detachable suppressor; I can move it from gun to gun as the mood/need suits.
RRA is a good choice as a host. They build a very well constructed basic AR. If you buy an integrally suppressed upper and it has a length of at least 16", you can just pop the takedown pins and go back and forth as you like. The RRA is probably $200 or so more than cheaper competitors, but is still better than some of the high end guns. They build a dedicated 9mm model which has a block in the magazine well that can be removed with minimal tooling (a hex wrench...included, I believe) and it runs the standard Colt pattern magazines or you can use modified Uzi magazines, which are relatively cheap. Another option is the Bushmaster Carbon-15 which is made of "high impact composite" (read 'plastic') and has the magazine well molded to take only the Colt magazines or converted Uzi variants. They are lightweight and available as carbine or pistol models. The latter would obviate the need to register it as a SBR since it isn't a rifle to start with. I have both versions and use the AAC can on them.
Olympic Arms builds two versions of dedicated 9mm guns. One uses a proprietary magazine that has extra plastic to fill up the standard AR magazine well. If you wanted to use the lower with a 5.56mm upper at some point, the conversion would be easy and will allow the use of mil-spec magazines. Their second option is a Glock magazine model that uses any of the Glock pistol magazines for the 9mm/.40 pistols.
Lastly, just about any AR lower can be adapted to use 9mm magazines. Some have a block with a paddle release, like that of HKs, that will allow the removal of the magzine. The problem with some of these is that they are not locked into the magazine well and actuation of the 'normal' magazine release will drop the entire unit, magazine and all, which makes combat reloads somewhat dicey at best. The original Colt adapter units required drilling holes in the receiver and driving in a couple of pins to hold it in place. They hold, but if you ever wanted to sell it to someone who wanted a 5.56 lower, the holes might kill the deal.
The AR15.com board has a whole forum section on pistol caliber builds. You might want to read some of that at your leisure.
And
www.silencerresearch.com will get you some relatively unbiased reviews of various silencers on the market. Keep in mind that there is really not an industry standard for "quiet" as test set-ups don't easily adjust for a lot of variables. But the reviews are still valid in most cases. Another option is ask on
www.sturmgewehr.com. There are a lot of folks there from the NFA community. They have as many purse fights as would be found on any board these days, but there is some good infomation to be had as well.
If I can help you, give me a shout.
