Gents, thanks for the comments.
Let me clarify what I have found:
On the Spanish civil war imports, almost all of these rifles were MK III and MK III B rifles. The numbers were not that high, only a few thousand at most. These rifles, if what I have read is correct, came out of the SovietUnion and were the residuum of the rifles that were supplied by the UK
to the Whites in the Ukraine during 1919 and perhaps some of the the Armenian rifles. One observation that seems to back this up is that none of the MK III rifles that can be traced to this import lot have the reinforcing bolt pin to prevent the bolt from being assembled incorrectly.
A dealer I know, who was 85 when I spoke to him and used to go down to Interarmeco in the day, told me that few if any of these Spanish civil war rifles had good bores, most were completely rusted out. He also indicated every MK IIIB rifle he had seen was from this lot. He also said this bad bore condition contributed to there being preserved, as the bores were so poor that no one would bother sporting them.
Leaping forward to the WWII disposition of the 90,000 Canadian war reserve Ross rifles. The comments on the Canadian destruction of Ross rifles might explain where some of the 15,000 remaining war reserve rifles in Canadaended up. Not all were destroyed as there are ads for sported Mk II and MK III rifles from the 1950s that indicate the rifles were surpluses from Canada. In any case that still leaves the problem of what happened to the 75,000 rifles sent to the UK in 1940 from the Canadian war reserve. These rifles were all MK III with the Ross rear sight, the reinforce pin in the bolt.
Why are there not more of these rifles about? As I said here in the US of A the MK II 3* seem to be the most common rifles, as 20,000 were brought in during 1917 for training rifles. MKIII rifles seem to be very rare here, and also in the other remaining commonwealth countries.
Compare that to the number of ex Navy Ross rifles, (many of which were sported). These rifles were released in the 1950s. There cannot have been that many, and yet these rifles seem more common then the War reserve rifles. (unless the Naval rifles were from the WWII lots and not remaining surplus from WWI).
Any insights or possible paths to pursue would be of interest.
FRS