I have Pabst fans in use, both 80mm:
Pabst 8412 NGL 26cfm@19dBA
Pabst 8412 NGML 19cfm@12dBA
These are the quietest fans I know, but also not the strongest. If you don't get your hands on one of them, try the Panaflo L1A, it gets pretty good comments in the forums.
Try a private message to Gizzo, he has his own website with most of the common fans!