The complete lists of supported MIBs on 6500 series is here: ftp://ftp-sj.cisco.com/pub/mibs/supportlists/wsc6509/wsc6509-supportlist.html
For interfaces, I believe the bridge-mib.my would cover a basic set of snmp objects. You may need to add the cisco-ip-if-mib.my, and entity-mib.my as well. Heck - why not just add them all and that way you know you have them?
Hope this helps. Please rate helpful posts.