The M1 had not reached the Marine Corps until 1942 — pretty much during the Guadalcanal Campaign. The ‘06 Springfield was still pretty much standard issue for the Marines & overseas Army units (Wake & the Philippines) at the outset of the War. Also there was a significant FBI counter-espionage case in the ‘30’s where a German spy was nailed trying to aquire the M1 technical spec’s. I admit I don’t recall the date of the Bust, but taken together with the slow fielding of the weapon you’d have to say that M1’s were hard to come buy for anyone outside US prior to Pearl Harbor. I’m not aware that M1’s were used in Lend-Lease, and that would be the only other mass outlet prior to the US entry in the War.
I’m no expert but they were sending Brits Lend Lease M-1 Garands starting in 1941. About 38,000 were delievered in 41-42. I don’t think it is a far stretch to assume that the Brits sent a few over for the gunsmiths of the Soviet Union to look at via the Murmansk run.