I expect this is a bootleg which is legal in Europe but it still sounds tasty.

"Live At The Matrix December 1970 (CD) by David Crosby With Phil Lesh, Jerry Garcia & Mickey Hart

Recorded before a small San Francisco audience as Crosby completed his classic solo debut (issued in February 1971), this superb set finds the former Byrd moonlighting from CSNY and collaborating with three members of the Grateful Dead on a mixture of standards and more recent compositions. The singing and guitar playing are outstanding throughout, and this release is sure to delight his many fans.

Tracklist.

DROP DOWN MAMA 4.20
COWBOY MOVIE 9.50
TRIAD 9.48
THE WALL SONG 7.56
BERTHA 4.16
DEEP ELEM BLUES 7.15
MOTHERLESS CHILDREN 9.14
LAUGHING 10.40"

Edit - already available on You Tube, it seems:

"During the rehearsals and recording sessions for If I Could Only Remember My Name, David Crosby and three members of the Grateful Dead – Jerry Garcia, Phil Lesh and Mickey Hart – played three dates at San Francisco’s Matrix club, December 15th, 16th & 17th, 1970.

These rare recordings, from an afternoon rehearsal and an evening live show, capture this unique configuration performing a variety of Dead, Byrds and Crosby material with pretty good sound considering the casual nature of the get-together. The afternoon session is a great, fly-on-the-wall band rehearsal, as Crosby leads the Dead core through arrangements of “Eight Miles High” and “Cowboy Movie.”

While there are instances of overloaded mics and sloppy exploration, once the band gets into a groove, and Garcia starts to take off, it’s a joyous sound indeed. The fusion of Crosby’s and Garcia’s styles is more pronounced than what would eventually be heard on If I Could Only Remember My Name… and is all the better for it. Blissed out expansions of DC’s “Triad” and “The Wall Song” are a delight.

The live show has circulated as the Dec. 15th show since it first surfaced, though the rehearsal is thought to be from the 16th, based on some of Crosby’s dialog during the tapings. The band alternately called themselves David & The Dorks, David & The Ding-A-Lings and Jerry & The Jets, but were originally billed at the Matrix as Jerry Garcia & Friends. There’s more Crosby in the archives."

[Edited on 10/2/2014 by Shavian]