Bumper comes off then you have 4 (or 6, I forget) bolts to take off the crossmember. - Expect to do some grinding/hammering to get it off I:
You VW parts dealer
VW heritage and Justkampers do them I think or a 2nd hand one via fleebay or off a van being broken. To be fair the rear crossmenber is quite hard to get hold of so you may end up using VW dealer.