There are not going to be many MiBs available for an ASA security device. You may use
http://www.cisco.com/go/mibs , then Non-IOS based mibs, then Security and VPN pulldown and pick ASA to view them.
Ultimately, I would just snmpwalk one of your ASA and store the details into a file, then search for what you are looking for. If you do not find it, then the answer is that it is not published via snmp.