Welcome.
19 is hard. If it was 14, you could cut the hex spot out of an old wheel and after adding a 12mm hex you would end up with a insert adapter that would work.
The only idea I have is a bearing or bushing 19mm od, and the id of your axle.
I'm working on a few trailers myselft, 1.55 and 1.9 wheel size.
Ofna and duratrax seem to have 19mm. Ofna is out, but there are "related" brands to ofna