I get mine for free! Little known secret-many business class PC's used them in their power supplies. I get so many AT power supplies I scrap them for their fans!
Many of these OEM power supply fans have a two pin header, different from a three pin only in pin count. You can chop off one of the location lugs to connect it to a three pin header. Three wire PS fans always have a wierd proprietary header.
What's the frequency, Kenneth?