Looking at the choices out there I can actually see a Thumper in my future:
CRF250
Royal Enfield
WK 400
Herald 250
MASH
I have 1.9 MZ's in the garage, but as Steff says, getting one going involves more than a quick trawl through Ebay.
If I had the time I'd buy a Chinese YBR 125 clone and see if they really are the CZ for the 21st Century.
Andy