I’d be surprised if you could source a spare, even from the manufacturer. It has spaces for the derailleur drop out bolts probably specific to that frame too so finding a generic replacement may be tough.
I would make one. Apologies if you already know the following…
Hobby vice, maybe a drill with bits, junior hacksaw, hand files and donor washer of the right size and thickness.
Then clean the area up and glue it in with a wheel in place to hold it while it sets. Which glue did you use last time? Maybe something very tough like araldite this time if not already, or perhaps Stormsure (which is flexible) if you used araldite before and that failed.
Good luck! Whichever route you decide let us know with pics!