"So the putschists have a army in Africa, no transport available and basically no options.
Problem: We don´t have a real civil war, just another failed pronunciamento."
Well, they sort of DO have an option. Franco was all but worshipped by the Arab troops under his command (he did various insanely-brave things during the Rif War and they thought he was "blessed" somehow). Perhaps the Nationalists seize control of Spain's African possessions and proclaim some sort of "true Spain" and insist that someday they'll return in triumph to mainland Spain (just as some Nationalists on Taiwan think they have a chance in heck of overthrowing the Communist regime).
I came up with that idea somewhere on the old board and it got incorporated into one of the "Big TLs" we had.
If WWII comes around, the Nationalists could emerge from North Africa to fight a war of vengeance (this assumes Republican Spain would be anti-Hitler and Hitler would see Franco and Co. as useful proxies).
Of course, with all of mainland Spain under their control, the Republicans could simply invade North Africa and "restore order"; however, if the Nationalists appeal to the Arab masses against the "dictatorship in Madrid," they might be able to start some kind of anti-colonial revolt (sort of like Louis XVI openly siding with the 3rd Estate against the nobles and the church). The Republicans were rather racist (I saw one of their posters...it portrays Franco as a puppet of Nazis, fascists, rich Jews, and, referring to his Arab armies, black Africans), so things could get VERY ugly.