Thanks a lot for your answer,
but so rare they are not,
you can find the original concerts on sugarmegs.org.
especially the "Tales from the mothership" or "Almost Starhipshape" concert
from the octobre 1970, one day after Janis Joplin died,
Marty Balin sings at the end of the concert,
got the revolution, I need a new band.
Oops, I didn't saw you mentioned sugarmegs already.
Here you can find the JA-shows from sugarmegs:http://tela.sugarmegs.org/bands.aspx
Have a lot of fun.