Mike
this is from the WLC below.
Q. Is it possible to set a limit to the number of clients that connect to the access point (AP) on the AP itself?
A. In general, there is no way on the AP to limit the number of clients that connect. The clients actually load balance between APs once they exceed the profile threshold value, which by default is 12 users. If you enable aggressive load balancing, the WLCs might disassociate some clients. Aggressive load balancing sets this threshold value at 3 users.
Radio Resource Management (RRM) load balances new clients across grouped lightweight access points (LAPs) that report to each controller. The controller provides a centralized view of client loads on all APs. This information can be used to influence where new clients attach to the network or to direct existing clients to new APs in order to improve wireless LAN performance. The result is an even distribution of capacity across an entire wireless network.
Note: Client load balancing works only for a single controller. It does not operate in a multi-controller environment.
Refer to Radio Resource Management (RRM) for more information.
http://www.cisco.com/en/US/products/ps6366/products_qanda_item09186a008064a991.shtml
Here is the link to the RRM configuration you will find client setting that will send a snmp trap to the Controller.
http://www.cisco.com/en/US/docs/wireless/controller/3.2/configuration/guide/c32rrm.html#wp1111872
hope this gets you pointed in the right direction.
Bill