I tried to find 60mm quiet thin fans once, and was largely unsuccessful.
The best solution that I found was to undervolt with a fan mate my 60x10mm Delta thin (4800 RPM CFM) to about 3000 RPM. Still moved some air, and much quieter. According to the delta specs, it would move 13 CFM at 24.5 db at 3000 RPM.
I did buy, but never really used, a FBA06T12L (15mm thick) from digikey.com (12 bucks! ouch). It didn't seem to be so great that I'd really recommend it, though it does have the panaflo name. Hope this helps.
Delta