I just ordered a G2Z lock-out tailcap and also the bezel (both in black) for my existing G2. The email I got from SF Customer Service asking about price says:
"Sir,
You need a 14334-1 cap ***'y, list price $5.06, and a 14401-1
bezel, list price $14.72
If you have any further questions do not hesitate to write back or call
us at 1-800-828-8809. We are dedicated to providing world-class customer service and welcome future inquiries or comments."
The earlier comment about the tailcap feeling "loose" is pretty accurate; it works, threads don't seem to be _too_ mismatched, but it does seem to turn easier than the stock tailcap (also my stock G2Z doesn't have quite this feel). The bezel seems to work great, so now my G2 has a pyrex lens to better withstand drops, the P61, etc.; and a lock out tailcap.
Total price $28 (G2) + $5 (tailcap) + $15 (bezel) = about $50 for a pretty solid light (+ spare parts). Of course, my G2Z (OD Green) I got for about $60, so no huge savings.