I'm not really an expert on the Dead archives, but you would probably have to have a copy made from the original multi-track tapes. Which are probably in the archives or the studio archives where the album was recorded. The chances of that happening seem slim, but again I don't know much about how the Dead archives are maintained.
Check out this link, the first song is Bobby and a drum machine, and then the next two are Bobby, Phil and a drum machine, then some rehersal stuff with whole band, now thats isolated tracks for ya ... plus it is just fun stuff, Bobby on Brother Esau is freaking awesome !!!!
You guys..of course are right the GD always flushed out new material live, sometimes for yeras before they recorded it, however I still find it odd that Booby would be practicing and or revamping a song he had played for2 years, in his apartment or wherever, when he probably was writing new songs at that time. Anyway I guess he just had some time on his hands.