My company (Lakamo Recruiting) specializes in Usability recruiting.
One of the most important criteria for Usability recruiting is having
recruiters who understand what Usability does, why it differs from
Focus Groups, and what are the challenges inherent to Usability
Smaller companies that get to know your recruiting needs will usually
do a better job. It is much more personal and the recruiters are paid
to think, not just to sit in a room dialing.