14mm is the classic oversize bmx threaded size.
Bmx shop can help you.
You could potentiality grind flats on the axle to fit a 10mm dropout, although of course the axle will sit 2mm low, and the nuts will probably tangle with a derailleur.
I doubt you could swap to a 10mm axle because of the cup diameter - so you probably need to get another wheel, unless you want to swap out the hub.