Yeah, point taken, 6 vs 5 spoke isn't going to line up well..
Alright, perhaps this is where Ebay might be a good possibility?
Found this there..
Although it looks like the spokes are set at angles on these caps..
Doesn't say what series but does say 5 lug which typically should be for 15" rims.
Can find them
HERE on Ebay..
You could also look up some of the RV surplus outlets in Indiana, bunch of those that buy up leftover surplus inventory when the RV manufacturers end of life a model..
You could also check with E-Trailer, their website shows they sell Hispec rims..
Perhaps they might be able to help?
HISPEC AT E-TRAILER LINK