Episode 28 still missing.

The SHANACHIE link no longer works - available on
the internet archive wayback machine:
https://web.archive.org/web/20080827164431/http://www.shanachie.com/artist/videos/rainbow.htm

to summarize:
605 THE STANLEY BROTHERS and DOC WATSON
606 JOHNNY CASH and ROSCOE HOLCOMB
607 SONNY TERRY & BROWNIE MCGHEE and MISSISSIPPI JOHN HURT, HEDY WEST,
    & PAUL CADWELL
608 NEW LOST CITY RAMBLERS and GREENBRIAR BOYS
609 THE CLANCY BROS. & TOMMY MAKEM and MAMOU CAJUN BAND
610 JUDY COLLINS and ELIZABETH COTTEN

Thomas.