Obviously some of the factions had relatively reliable foreign support such as the Kuomintang with the Soviets and later the Germans and the Fengtian clique was 'sponsored' by the Japanese but how did many of the other Cliques like the Anhui, Ma or the Sichuan and Guangdong Warlords keep their men supplied with weapons and ammunition to wage their wars?
Did they subsist on occasional bouts of foreign support or were their independent arms dealers for them to buy their needed equipment from?
A bit of both, really. They sourced their weapons wherever they ca. They did hire a fair bit of foreign advisors and also a few also hired small groups of foreign mercernaries. Many of these advisors bought weapons with them too to China. Some Ex-White russian soldiers, having fought a losing war against communism in the soviet union, did went to Shanghai and subsequently served as mercernaries and bodyguards for various factions and cliques.