from what i can see , you need to snmp WALK: 18.104.22.168.4.1.25053.1.2.2.22.214.171.124.1.3
when i walk that, i get 216 x OIDs , each with a 1 or 0 (ie status connected or disconnected). this lines up w my ZD having 216 APs, and about 6x of them are curretnly disconnected.
however the issue becomes how do you monitor 216x OIDs via a snmp device (like PRTG or MRTG).
what i do is monitor: 126.96.36.199.4.1.25053.1.2.1.188.8.131.52.0
which is generated on/from the ZD and returns a # for current connected APs to the ZD (so if you see a drop then you know some APs are missing/disconnected).
its the opposite of waht OP wants, but can accomplish the same thing. (if you use PRTG you can use sensor factor to subtract this value from a static # you input, of your total active aps, ie in my case, 216 - = # of disconnected (or 0 if no disconnected aps)