I see your point...
I'd say posting a WTB on Sturm for a USC or UMP cocking handle ( or the whole handle tube assembly )
Also do a search there for small USC/UMP parts.
There are some de-milled UMPs floating around...
There is this site where they are selling de-milled UMP .40s >
De-milled UMPsThey may or may not "part" with the cocking handle...
Or you could contact this dude, which "some" people swear by >
HKpartsonlineThen there is Adam , Hk4ever (spelling?) on this site... he deals with the MP5 parts... he may be able to get a line on some USC or UMP parts. I'd give him a try too.
Then there may be the top-notch option.... I have no idea, but they might make a US made cocking handle. Don't really know for sure though.
I am sure you have entertained most of the above.... but if I were you I would try sturm and hkpro first off.
If all of the above fail.... get your shit sent to HK quick before they start or complete their move/transition to AL. That could throw a wrench in your works for a long time
Good luck, let us know how it goes.