Actually a copy of British Vickers 6-ton, T-26 was the most successful tank of its time, so being extensively exported by the USSR to other countries. The Spanish Republic purchased some 281 of them --all belonging to the single turreted type B.
They were perceived by he Nationalists as so dangerous that a public reward of 500 pesetas of that time was offered to anyone capturing one. About 2/3 of the Spanish T-26 were destroyed during the Civil War, while most of the rest were captured by the Nationalists, being kept in service after war well into the 1950s.
Seemingly, one true Vickers 6-ton Mk. E type B was purchased by the Spanish Republic to Paraguay through an arms dealer --that tank was a war booty, captured by Paraguay to Bolivia during Chaco War. Once in Spain, it was most probably modified so as to become a standard T-26.