I was in a similar predicament in the past when my transfer case locked up. I wound up calling around to the DSM performance shops i.e JNZtuning, JMF, STM, etc and was able to find an output shaft that JNZ had lying around. Otherwise Jack's Transmission offers them on their website but they are a bit pricey.
As far as installation is concerned it is fairly straightforward. Just take your time and be patient.