Could I make an ACT “superscore” for colleges to see, just like I could for the SAT?
No. You send the multiple ACT scores to schools. Those that superscore will do so themselves.
Do CUNY schools superscore the scores themselves?
The most complete list I know of: http://blog.prepscholar.com/colleges-that-superscore-act-complete-list Unfortunately there isn’t a full list like College Board has for the SAT (though that can have errors too)