If it was a System7/NS2 USP then for sure it will be the same hop up rubber as the Glock (Sys7/NS2 is based off the KSC Glocks gas design).
Worst comes to worst Aquamarine *might* be able to source you a hop up rubber from one of the various small airsoft shops in Japan.
Otherwise if you're going to HK or know anyone going to HK there's always the shops on Kwong Wa street that have little doodads and random parts here and there if you (or your friend) are willing to look.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE