I think the most similar experience you came to the International Brigades would have been the Cuban guerilla units that fought across the globe with local communists and peasant anti-colonial movements. I think it'd be interesting if more figures like Fanon survived to join Che and others in travelling to specific countries in turmoil to fight for socialism and anti-imperialism. You could have Cubans, Algerians, Irish Republicans, maybe groups like Baader-Meinhof or the Red Brigades and other anti-imperialist fighters all fighting in the same organisation.... cool to think about but perhaps not so plausible.
Another thing to note, Spain was an isolated incident (relatively) whereas, after WW2, there were ongoing anti-colonial wars springing up all over the place so there was never any real focal point for international brigades to converge.