Did a little digging and saw a few similar, but not exactly like it. So establishing the brand as a first step in the search didn't happen.
Didn't see any sources for parts for that type of gun, though some non working parlor guns were being sold as parts guns.
You might have proof marks that may help with identification.
This one from an old auction reminds me of yours a little, but they don't know what it is either.
German made 4mm parlor gun/awesome For Sale at GunAuction.com - 8119461
More than one person has said the US CB22's are more powerful than the primer-only European ones that the guns were designed for, and shouldn't be used.
The square butt and lifting block action (Warnant action) seem to be more rare.
Five years ago, someone in a forum looking for parts for their Flobert parlor gun was directed to:
Jack First Gun Parts
There seems to be some Flobert knowledgeable folks on the antique firearms collectors forums. Even some with spare parts to share.
Didn't find your part, but enjoyed learning some of the history of it.

Interesting little piece. Good luck in your search.