I have found this excellent article on the guns used in the Spanish Civil War:
The author, Dan Reynolds, says:
In 1956, the Spanish Nationalist Government of General Franco sold the rights to the stocks of Red armaments captured during the course of the conflict (1936-39) to the firm “Llama”. The small arms were acquired by Interarmco and many imported into the USA circa 1959-62… The remarkable thing was that the number of M91/30 rifles was proportionately low considering the large numbers supplied. Possibly the bulk of the surviving M91/30’s were acquired by some government.
Related to this, I have read elsewhere that Spain sold many rifles in 7,62 x 54 to Finland after the Spanish Civil war, including the Remington and Westinghouse Mosins in stock.