I haven't been shopping for a T56, but I would imagine that there are plenty laying around these days. Keep in mind that it has a 6th gear. In addition to that, it is a strong tranny. Bolting an inferior t5 out of a 2.8, after changing the bellhousing and then maybe the hydralic clutch mechanism, and the flywheel and the clutch and pressure plate, maybe it's cheaper and less work to spend a few more dollars at the beginning of it all.

Remember, the cheap and the poor always pay twice. But then, what do I know.