Green’s Dictionary of Slang

co-ro n.

(Aus./N.Z.) a co-respondent (in a divorce case).

[Aus]Sun. Times (Perth) 27 Nov. 4/7: Now the bookie is alleged to be the Co-Ro in the impending laundry work at the Divorce Court.
[NZ]Truth (Wellington) 22 May 7: A railway signalman who was bracketed as co-ro.