The best place to start would be the various "Mexican Adventure" lines of figures. They'll give you armed peasants and basic Republican infantry and cavalry. Some figures for the Revolution can be used post 1970s, notably the Rurales, who wore a grey uniform based on Vaquero dress. The available figures give them bandoliers, which did not come into use until they got weapons with brass cartridges.
As for "The Undefeated", Wayne was captured by Juaristas (Republicans) but actually fought French. As did
Charleton Heston in "Major Dundee". But don't use either for uniforms. Look again to the Maximilian lines for some French, as well as Crimean, FPW and even ACW (for Zouaves) lines. Lots of variety on Maximilian's side.