There were at least 4 of the ST 27's in Sudbury, Ontario. They were mothballed by Voyageur Airways, after they aquired the aircraft a number of years ago.
I don't beleive Voyageur ever put them in to service.
I also understand that the balance of the aircraft were returned to the factory for dismantling.
I also worked for a company a few years ago that looked at the ST 28 aircraft.
One of the reasons the aircraft was not mass produced... where the wing spar crossed the fuselage it created a "hump" at the mid point of the aircraft.The US government would not certify the aircraft to operate in the states. There was also some politics behind the certification, it was major competition to the Beechcraft company and the development of their 19 seat aircraft.
"Avro Arrow all over again"