Download Pica8 supported publib MIBs here:

Supported Public MIBs.zip

The publib MIB SNMP-USER-BASED-SM-MIB is supported from PICOS 3.6.0, for details about this MIB, see http://net-snmp.sourceforge.net/docs/mibs/SNMP-USER-BASED-SM-MIB.txt.