Boom, try this link. I've used it for quite some time when shooting military aircraft. You'll need to have observed the AF
Serial number, but once you have that, and of course know the type, you can quickly find the cn in most cases (sometimes cn's aren't listed, but that's rare):
For example, Lockheed F-16D, AF
Ser 94-0274, cn DB
-1, went to the Singapore Air Force.
Hope you find this useful.
United States Navy submarine sailor turned aviation photography geek.