Clive Law wrote that inventories showed 385 scopes and 208 rifles in store in Canadain the 1930s, and reproduced a letter from the Canadian MGO to the then Chief of Staff suggesting making up additional bases so that "nearly 400" sets could be put into service for training; no date is given, or reference for the letter cited, but presumably this was in 1939.
And so Law states, "a programme was instituted to manufacture, at the Quebec Arsenal, 177 additional mounts to allow for as great an issue [of complete rifles] as possible...". (385-208=177)
Law states that the 80 scopes brought to the UKby the 1st Canadian Division, "...then had the mounts removed and new mounts made to fit the No.3 Mk.I rifles...." He also states that in May 1940 an additional 80 W&S sights were requested", but he does not say if they were in fact delivered. Clearly a misstatement to say that the mounts were "removed" as if they had been present there would have been no need to make up 177.
So, taking that 80 from the 385 scopes in store, we have 305 left and at least 211 rifles. However, we know some new bases were fitted to Ross rifles in Canada as an inventory in December 1943 showed "267 rifle and sight combinations in Canada", this "...despite continuing deliveries to the Canadian Army (Overseas) of the W&S sights..."
No reference or details are given of these "continuing deliveries", but presumably it cannot have been more than 305 - 267 = 38. Personally I doubt there were any more than the original 80 sent, unless something less than 38 for spares or replacements, and logically more of those would have been needed in Canada than in the UK.
Not impossible that more scopes were later found in store somewhere in Canada though, considering the rifles and scopes were at one point stored in different provinces! Also, 115 (500-385) does seem like a high loss/scrap rate, considering most of the sets didn't go to Francein WWI and we have no evidence of even training use in Canada or the UK. However, the scopes that saw service in France may have been scrapped as BER even if they weren't just because no one wanted such things in the years immediately following WWI and there was no money to overhaul them. That said, there are so many mechanical weaknesses in the design that correcting for wear and tear in the mounts was difficult if not impossible; wear in the adjusting cam particularly.
Making up bases for the P14 would have been easy enough for any one of thousands of little firms in the U.K. at that time. Fitting would have been a bit specialized, but there were armourers with the skills. Could also have been done at RSAF Enfield, or contracted out to the gun trade. The 1st Can. Div. arrived in the UK in December 1939, so the work might have been done in early 1940 when the Phony War was on and firms were operating more or less on a peace-time basis.
If I had to bet, it would be that they were done in the Canadian workshops in the UK. RSAF(E) was working on the No4(T) ex-trials rifles presumably, so doing them "in house" would have avoided a lot of bureaucratic delays probably.
The only other possibility I can think of is that ex-Springfield bases could have been purchased in the USAand modified to fit, if that was required. I wouldn't be surprised if the surplus dealers in the USA still had hundreds if not thousands of W&S scopes on hand, and probably most went for scrap once the USA geared up war production and scrap prices rose.
Or possibly the "Quebec Arsenal" made up the P14 bases in the event, since they definitely made up some for the Ross Mk.III and we know that unless more scopes were found in store, 177 bases for the Ross Mk.III were not needed as 177-80=97! The very fact that 177 precisely were ordered suggests no provision was made for spares.
Somewhere in the files there should be press/PR photos taken in 1940-42 showing those P14's being used in training in the UK, if they had been completed in 1940-41.
If someone was to dig into the records of RSAF(E), now presumably at Leeds, there might be some clues about this. And of course there might be more in Canada as well.