oooh thanks for those links Megalodon...nice sources.
i was only looking at aircraft that were still in active numbers through late 41/early 42, and not including all of the ancient crates invovled in the sino-japanese war. according to the second link you posted, the hawk 2 and 3 were pulled from front line duties by 41, and according to another source, the remaining serviceable i-15bis were pulled by the end of 1940 in favor of i-16s.