Here are some I had in a document...

3rd Generation Model Codes

39xx = single stack 9mm
59xx = double stack 9mm
69xx = compact double stack 9mm

10xx = 10mm
40xx = .40 S&W
45xx = .45 ACP

xx0x = full length barrel TDA
xx1x = compact barrel TDA
xx2x = full length barrel Frame Decocker
xx3x = compact barrel Frame Decocker
xx4x = full length barrel DAO
xx5x = compact barrel DAO
xx6x = mid size barrel TDA
xx7x = mid size barrel Frame Decocker
xx8x = mid size barrel DAO
xx9x = Special Order

xxx0 = Scandium frame
xxx3 = Alloy frame silver
xxx4 = Alloy frame black
xxx5 = Steel frame blue
xxx6 = Stainless frame
xxx7 = Stainless frame Slide Decocker
xxx8 = Special Order

It is actually a very effective coding system for administrative purposes. The only problem is that the Performance Center also makes custom guns based on the 2nd Generation frames, which used a 3-digit code.