It seems that if you want a reproduction late-war German experimental rifle design, you should get in touch with GunLab’s Chuck. Besides his VG-1-5 project which we’ve covered several times in the past, he also mentioned a year ago that he was doing a run of 60 Gerät 05 rifles. These were roller-locked gas-operated rifles patterned off the Gerät 03, which was itself a derivative of the G.43/K.43 (and they, in turn, were derivatives of the G.41(W) rifle). They fed from MP-43 magazines, while having a conventional stock layout.
A result of that project was this cutaway Gerät 05 rifle, which is almost certainly a unique specimen:
For those interested in more information on GunLab’s Gerät 05 project, they can read Chuck’s other posts on the rifle here, here, here, and here. Forgotten Weapons also has a family photo of the roller rifles. While it doesn’t have ever member of the family, it does have most of the experimental ones (reproductions of them, anyway).