They show up on Ebay on occasion as do other parts for the M/Schoenauers.
M/S parts for the commercial rifles and carbines are very pricey as a general rule..
The Military Greek M1903 M/S parts will fit for the most part but that doesn't get you into the commercial rifle& carbine stock accessorys like the carbine forend cap , forend clevis swivel, ect.
This place adv they have M/S parts, but I have never dealt with them
https://sellgunparts.com/mannlicher-schoenauer.
I have a very few M/S parts. I will check and see if I have an extra forend cap. I know I have one, that's supposed to go on a 1903 project carbine.