[veltro]

By the date of 27 April 1945 there were no German Bf 109s operating in Italy apart from those of NAGr.11 based at Udine - Campoformido, several hundred kilometers from Milan...!

Since the only unit roughly operating in that area was 1° Gruppo Caccia ANR, whose Bf 109s were marked with all-Italian markings on fuselage, I seriously doubt that the source could be that unit.

One possibility is that the piece was recovered in one of Italian factories in Milan area that were known to be working for the Germans (Agusta for example), repairing and reconditionings their planes, and that the tail in question possibly belonges to a fuselage of a Luftwaffe aircraft (or parts of it) still being worked on or left abandoned in some workshop...