I'd guess the ledgers are in the old Suhl jail, but that's just a guess. What specifically are you searching for besides the above? More about the modell Neptun? Does it have ejectors and what type tube steel? The original cost would be say 600 RM plus any additions so does it have a cartridge trap, horn triggerguard bow, etc.? I can list the extra cost for different tube steels if anyone fancies that.
Was it Richard or Franz Schilling you had in mind? I believe Franz Schilling was a engraving source staple for Sauer so I'd think he is out but it might be Richard Schilling. For now, my vote would be for Franz Schamberger.
Kind Regards,
Raimey
rse