HOPL III is here: http://dl.acm.org/citation.cfm?id=1238844&coll=DL&dl=GUIDE&C...
HOPL I is here: http://dl.acm.org/citation.cfm?id=800025&coll=DL&dl=GUIDE&CF...
I have the hardcopy versions of I and II that I bought used from Amazon and they're great.