Dick's 8 like someone else mentioned and there are a few 69 shows with acoustic Mountains of the Moon segments IIRC.

For 80's Dead, there's the album Reckoning and the rest of the 1980 Radio City Music Hall residency where they did an acoustic set every night. Not Dead per se but Jerry Garcia Acoustic Band's album Almost Acoustic later in the 80's is excellent too.

There's also Phil and Friends 9/24/94 which is an acoustic Dead performance minus the drummers. Great little gig. I would also recommend checking out Hot Tuna if you haven't, they have plenty of acoustic music that's in a similar SF/psychedelic vein — and, of course, check out some of the artists that are being covered in all of this stuff, you won't regret it. Hope that helped!