So doing some more digging ... basically, this page says the WLC supports only the CISCO-LWAP-xxxx and AIRESPACE-xxx MIBs related to wireless functions. The LWAP functions did not point me to any direct association objects.
Some on this forum suggested to others to try the AIRESPACE MIBs. But the suggested OIDs only give an entire row entry (instance number) for each client with no index of total clients. Those instance numbers are based some client info (not sequencial) so even to look at them via static OID is impossible. So you would need to know the instance number for each client with does no good. This was apparent by using and SNMP browser on the WLC.
In browsing the AIRESPACE-WIRELESS-MIB.my file directly, I found A POSSIBLE SOLUTION:
"No of Mobile Stations currently associated with the