Early in the war (1937, etc.) many of the better KMT divisions were trained and equipped by Germany, wearing German kit with puttees. Later in the war, many were US trained and equipped. But Japanese in caps might do too. At 10mm scale, most of your conversions would be with the brush. With luck, someone out there has some other ideas too. My main 10mm source is Pendraken.
Korean War North Koreans in cap might do. Irregular make 10/12mm modern bush wars figures in caps. They are armed with AK47s. If you don’t look too close…
I’m not aware of anyone making guys in baseball caps and puttees, but that would be just the thing.
This too shall pass