On my quest to find some over sized VW pistons for a reasonable price, I visited tons of online shops. One supplier that I found on the VW Vortex TDI forums was The Dub Doctor. What I thought was going to be a quick phone call about pistons turned into a 20 minute conversation about TDI engines and what would be required to rebuilt my engine.
Needless to say I ordered the pistons from The Dub Doctor and plan to get most of the other parts from them. I highly recommend you talk to them if you need VW parts for a TDI conversion of your own.