Research, you say? Interesting….
…so the only ones I know off the top of my head are Folk Songs For Folk’s Who Ain’t Even Been Yet and Solar Sailors, both Fish albums; according to fanlore they were the first commercially released filk albums (1976 and 1977, respectively). They were re-released together as Folk Songs for Solar Sailors, and if you don’t have that already, I highly recommend it.
But I’ve said several times, I’m not really qualified to run this blog, and if you want more knowledgeable people who know more than two things, you should go bother @animatedamerican or maybe @sci-fantasy