CISCO-SYSTEM-EXT-MIB.my is a good place to start and you can determine the OID from the MIB.
Once you feel as though you are on the right track, have a look at:
http://www.oidview.com/mibs/9/CISCO-SYSTEM-EXT-MIB.html
I gather that what you need is:
1.3.6.1.4.1.9.9.305.1.1.1
and
1.3.6.1.4.1.9.9.305.1.1.2
Enjoy.
Stephen