Don't think wire gauge is all that important since the meter does not read current. eBay has some nice 20 amp, 1kv probes for under $4 for the set, free shipping, from Duluth, Georgia, item # 235227227887. If you cannot salvage the old pin jacks, just cut off the banana ends and tin the leads. The binding posts will accept either.
The real McCoy is CX-1331/U also on eBay, item # 204419918731 but are a bit pricy @ $43 + shipping!
BTW, in TM-11-5511 the parts list for the leads, W1 and W2, are in Appendix II on page 69 but as you say, no AWG is called out.
Jim
Logic: Method used to arrive at the wrong conclusion, with confidence. Murphy