Driveshaft bearing wear normally manifests itself most when under load as a judder. I had mine fail a couple of times but I only felt it under hard acceleration. It should be driveable as long as you don't put too much load on it.
A quick look round and I agree it doesn't seem easy to get hold of a complete driveshaft. Buying s/h can be problematic because there were subtle differences in length and if you don't get the right one, it will pop out. If you do go the s/h route, make sure that the replacement driveshaft is put against the old one to check the length is correct.
Assuming though it is the tripod bearing and not the cup that is worn, then it should be OK to just fit a new tripod bearing.