This coolant tank is unique to the later 2001-2005 models, with the 24 valve engine. For those models with the 12 valve engine, see below.
This is informational ONLY, as VW has dropped this part and there are no other sources.
Update: May 2016: This item is now obsolete from Volkswagen and is no longer available.
You can use the earlier 1992-2000 expansion tank, although you will have to custom fit a longer hose to the radiator overflow, as the
hose nipple on the tank is approximately 180 degrees off. It will still work fine.