Middleman Minority Diasporas and Over Representation in Communist Movements

It appears that ethnic Chinese were disproportionately over represented in the ranks of the communist parties of Indonesia, Malaysia, Thailand, and Burma during their hay day in the 1950s and 1960s. I haven't been able to find solid statistical breakdowns of the exact ethnic composition of these parties, however. So if anybody has any suggestions of where to look for this information please let me know.