Bump up for visibility.
our NPM poll couple of MIBs for HW health data. There is one - corporate MIB that is common for various HW vendors and provide info about chassis & sensors. It's called ENTITY-MIB SNMP MIB and what you need to do is validate if your 3com devices support such MIN (for example via SNMP browser tool).
I can also recommend this page: Free MIB Download Search MIBs SNMP - Free MIB Download - OiDViEW IT Management Tools where you may select your 3Com vendor and check supported MIBs for OIDs that represent chassis and temperatures sensors. If you have a possibility to reach 3com, I would try that too since they may have this already documented.