That's a good question.
For current :
http://web1.whs.osd.mil/mmid/military/miltop.htm Rank/Grade link (iirc)
As for the number of "Ex's", ....who knows? It doesn't matter, really. If the "Anti-Rummy's" can't make enough racket out of the pool of ex-Generals; then there's, like, a jillion ex-colonels and Majors out there to cherry-pick from. They will have plenty of ammunition.
LOL ... the Good News is: "All the ammunition in the world will not make a bit of difference." Rummy has to please one man. That's just the way it works. :)