I came across a Rietschle 2688CE44 series pump in my "collection". It's a pretty high-end pump in the $600-700 range, but I often see them on ebay for $150-200. I came across mine in an auction lot of spray parts (bought the lot of parts for a sonic cleaner and got the pump for free). I figured it might work as it's high CFM (for a small virtually silent compressor) at roughly 3.0CFM @ 18psi. Only downside is that it maxes out at 25psi, so it will kick on pretty often as it can't really load the 5gal tank I have for it. That's fine by me because I basically just wanted it to be silent when off the trigger.
Right now I'm at the stage of shopping for pressure switches. I'm leaning towards a digital unit I found that has programmable high/low set points.
I'll post some pics as I progress. I just thought somebody may be interested.

Dennis