Try giving Falcon Northwest a call. They build high-end custom PC desktops and laptop computers. They have some really nice, quiet fans that might work for you.
I like Zalman quiet case computer fans, which can be run off a 9V-12V wall wart. I use one to cool my enclosed HT system rack. The rack contains two digital cable boxes which generate a substantial amount of heat that needs to be vented 24/7.