There's a number of "silent" (aka quiet) computer fans available, and one should fit your needs. You'll just need a 5 or 12V power supply to run it. Panaflow is often considered to make the quietest, but things like Vantec Stealth fans are more easily available. A temperature controlled fan might be useful as well, depending on your application, but I often find that they are louder than other fans at similar CFM rates. Check your favorite computer parts website. I've ordered fans from www.bestbyte.net in the past as they had fairly good prices on what I was looking for. I believe that there's a web forum dedicated to silent PC's, but I can't seem to remember the URL right now. I'm sure a web search would turn something up.