I know that IAABO is the only game in town in Connecticut. The local boards handle all of the assignments statewide (with a few exceptions for private schools, I believe).
While most IAABO members work high school games, in the end it is simply an association of any "approved" basketball officials. They generally don't assign college games, but I know that the local IAABO board has at least a few college refs (D-I through JUCO), and one NBA ref.