The Cabe’s eBay store has them for Magna pedals - possibly same size?
Success!!! Thank you so much for the suggestion!
Yes, the CABE eBay store "round replacement reflectors for Magna pedals"
do fit the assorted postwar pedals by Monark, Murray and likely others!!!
These repro replacement reflectors are a bit "thinner" than the originals (at least with respect to the Monark / Murray pedals), so once installed, they tend to move around a bit and rattle, but this is easily fixed with a small shim of some type.
I haven't yet figured out a good way to shim, will post once I have. At the moment I'm thinking of trying a piece (or a few pieces) of thin, clear plastic, cut to the same size circle as the reflector, placed behind the reflector. Or possibly a thin o-ring, roughly the same size as the outer diameter of the reflector.
The below pics show an original reflector insert from a 1950's Murray pedal (on left) and the "round replacement reflector for Magna pedals", sold at the CABE eBay store (on right).
While these repro reflectors aren't dead-on perfect duplicates, they are close enough and are a very quick, easy, inexpensive way to get your original postwar Monark or Murray pedals looking like new again (assuming your original reflector inserts are broken or missing, which most are).
NEW Magna pedal round replacement reflectors / CABE eBay Store