the germans did ship some equipment to china up until 1937 when japan went full scale into the “china incident” undeclared war. so players probably could excuse any equipment mix up to and including pz 1s. for a twist, there were some reports of german advisors actually leading kuomintang troops, so you could even slip a german leader into a scenario. the germans actually tried to help mediate an end to the war between china and japan, but failed, and by 1938 pulled out of china militarily, although the full break didn’t occur until 1941. german sympathy during china’s solo stand against japan was actually pretty high, with one famous example of the german consul protecting chinese nationals in the german compound from the japanese.
until the burma theater opened up, the best kuomintang troops remained those that were german-trained and equipped, at least until american aid finally arrived much later. so until american aid came there was a hodgepodge of german, soviet, british, french, and italian weapons in china. but as a result of the casualties from the battles of shanghai and nanking, late 1937, all kuomintang leaders and equipment would be pretty stretched.
however, kuomintang troops in early 1942, while british and american forces were being swept away in the pacific, and before much american equipment arrived in china, was still able in changsha (central china) to defeat a determined japanese offensive. so there should be some decent historical scenarios there with the presently available miniatures.
around and after 1940, there were also japanese-led puppet chinese troops, equipped with second-rate japanese equipment against the kuomintang, but who could turn against their japanese handlers, if anyone wants to set up rules for double crossing…
another possibility is using soviet pieces in china, since until 1927 the soviets were directly advising the kuomintang, and even afterwards aided the kuomintang against japan, when it suited stalin’s foreign policy - which explains the kuomintang t-26. but that would probably take more booster sets.