There are a lot of computer fans with more than 2 wires. Normally the second wire is used so the bios, and/or motherboard can monitor the RPMS of the fan. There are also some that have varaible speed based on tempurature, which is also not what you want.
Just get a normal 2 wire fan from radio shack or a computer store. Look for low noise, and low CFM I would not get one with a CFM over 20, and 10-14 would be better. Also small fans can get.