I was bored during lunch today so I took a stab at this.

Using the production numbers posted on the C-I-C-C-I forum:

Crossfire Technical Documentation

If you follow the link above to the C-I-C-C-I forum you can download the PDF file. I think it is in a public section of the forum...

I come up with 50508 crossfires (all sub models) left using a 4% attrition rate year over year. It's rough numbers but should be a good estimate.