Does OS X not capture the bssid of wifi networks it connects to? The only method I managed to figure out how to get that information is by polling the current system configuration via

/System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport -I

and/or CaptiveNetwork api’s (https://developer.apple.com/library/ios/documentation/SystemConfiguration/Reference/CaptiveNetworkRef/#//apple_ref/doc/constant_group/Network_Info_Keys).