It seems that rebuilt or new turbos for the 1.6lTD are no longer available through the VW dealer. (Not that you'd want to pay their exorbitant prices anyway.)
You could call around at the various turbo rebuild shops. Some keep an inventory of rebuilt turbos ready to go, or rebuildable cores they can build for you on request. Who knows, you could even happen across a brand new one. The identification number for the Garrett turbo off the 1.6lTD is "TA0304B", and the 1.6lTD KKK turbo's ID is 53249706080. As just one option for a turbo rebuild shop, you could try this place, I know they have a lot of inventory:
http://www.adpdistributors.com/There is also e-bay, this board's classified section, etc.