If you want to get a 1.9 TD (IDI) on the cheap, you'll have to travel north to get it. They were never offered in the US. Sometimes miracles happen: my dad found one in Maine while we were on vacation for $500. Installed it and it ran fine.
But, figure you'd have to drive to Canada to get one, and it's bound to be covered in scaling rust on the outside.
The other option that many people here seen to have taken (jimfoo, tintin, etc), is to convert a 1.9 TDI to an m-TDI. Basically, they've removed the electronic components in favor of a purely mechanical system. The benefits are more power than a stock 1.9 IDI, and greater potential for increased power. The downsides (as I see it), is fabricating an injection pump to work with high enough pressures for the Direct Injection style injectors, and fabricating a mechanical control for the Vairable Nozzle Turbo (VNT). You'll want to do this (as opposed to installing a stright turbo) as the VNT provides consistent boost thru almost all RPM ranges (not just at higher RPMS).
The upside to the m-TDI is that 1.9 TDI motors are more readily available in the US, its power potential, and the lack of electronic crap. The downside is the cost to do the conversion: longblock $1000-2400, custom pump $400-1000, etc. Of course, you could always just keep the electronic controls on the TDI and have easy HP gains with chipping and injector nozzles.
So, you have to pick your poison. High cost but easily available (1.9TDI), or lower cost, but you have to travel to get it (AAZ 1.9 TD).
As far as finding parts for the 1.9TD, it can be done here in the US. You have to do some searching, but they're out there. It probably easier than trying to find an actual longblock.