Axle slot fillers? Puch mtb

what is the correct name for these slot fillers and where can I get some?

I’m going to dig through the bins to see if I can find some spare metal ones that were used on clamp-on derailleur hangers.

This is off an old Puch mtb, got it posted locally currently but the more I look it over it does have some interesting features about it (like the rear derailleur cable being routed through a hole in the rear underslung brake post), so I might decide to pull the ad and keep it for awhile. I’ve never had a Puch before.

I don’t know why I bought this thing, but I did, do I really need a reason other that that it looked interesting???

Anyway, before I get out a carving knife and try to carve a pair of these out of an old piece of 2x4 lumber, where can i get some of these gap filler/spacers? Sliding the rear wheel all the way back does not work due to the rear brake arms not allowing enough adjustment for the pads to slide far enough, so the rear wheel does need to be positioned forward in the dropout slots.

I even considered running a 700c hybrid wheel in the back which might work, but would be stuck with the 26” wheel on front which might be a bit too weird to do.