Can you clarify "blocked access"? Do you mean that you would like to know when someone attempts to login to the sensor? If so, there are other ways to do that like looking at the audit logs. Or you could use TACACS and then configure TACACS to send a syslog event if you need to see this behavior real-time.
As for SNMP, you may want to have a look at the MIBS. Most of the MIBS are entirely hardware-based, so there doesn't appear to be a way to look at the audit logs on the sensor via SNMP.
Here is the link for the NSP MIBS: https://kc.mcafee.com/corporate/index?page=content&id=KB55030
Hope this helps you.