I ran total numbers and came up with the following: Total pilots in the FAA database with a certificate (Student, Recreational, Sport, Private, Commercial, or ATP), using the
USA as a "country" (the database does include foreign pilots with an FAA certificate and I did remove them from the pool), and disregarding medical expiration date I returned 526,506 certificates. When I selected just ATPs in the USA without regard to medical I returned 111,746. CMEL with an instrument rating (no ATP) without regard to medical, I returned 72,513. The combined of the two is 184,259.
You can search with a limitation on the medical expiration. I choose limit the pool to those with medicals initially issued as first class that expired or will expire in 2009 and 2010. The number of ATPs is 76,257. The number of CMELs with an instrument rating but no ATP is 18,054. The total of the two is 94,311. That number at the end of 2007 based on my search with the same methodology then was approximately 104,000. If you add in the pilots that meet the above with a medical that expired in 2008 you would add 9906.
Here is a link to the FAA database through Landings.com which has a fairly good search engine:
Landings: Aviation's Databases
I used APC data for the current number of employed pilots. It didn't take that long to add them up.
While the actual numbers are interesting and debatable, using the same methodology in Jan 2008 and now I come up with about the same number of "available" pilots in the pool.