Hi,
One Idea could be,
You may tweak the "Column List" by clicking the "+" symbol on top right hand side under Network-wide->Clients. [Screenshot attached for reference]
Thereafter you may download the list as CSV file. Filter the content in an Excel Sheet as desired. Copy the List of MAC Address you need to block and Apply "Blocked" Policy for them.
[Screenshot attached for reference]
You may also block devices automatically by assigning a "Blocked" group policy on the basis of "Device type" under Wireless->Access Control. [I am not sure if this what you want though]
[Screenshot attached for reference]
I do not see an option of alerting the blocked devices. However you may display a custom blocked message under Network-wide->General for the Blocked Devices.
[Screenshot attached for reference]
Regards,
Ajit
AjitsNW@gmail.com
www.ajit.network