Seriously, except for getting stranded, having those wheels stolen would be considered a favor.
But if you insist, there are shops, hardware stores and industrial fastener suppliers, that specialize in esoteric nuts and bolts. Find one of those stores and take your wheels in to have the axles measured.
I'm rehabilitating this bike into my NYC metro bike.
I'd like to replace the existing axle nuts with tamper resistant nuts.
What is the nut size and thread specification?
It is close to an M8 x 1.0 ... but not quite.
Have you considered replacing the existing axles with a 'new' axle & cones whose threading matches the tamper resistant nuts that you want to use for one-or-both wheels?
Seriously, except for getting stranded, having those wheels stolen would be considered a favor.
But if you insist, there are shops, hardware stores and industrial fastener suppliers, that specialize in esoteric nuts and bolts. Find one of those stores and take your wheels in to have the axles measured.