Yeah, hard to find the earlier work on CD but very rewarding. The material with Lasse Werner that came out as a Jazzland LP is, I believe, now available on a Dragon CD and is well worth seeking out. Numerous alternates and additional music really line the platter there.
Stockholm Dues is his second LP as a leader and is excellent. It was reissued on CD a while back (as well as going through a few different vinyl iterations). Agreed about the groups with Tommy Koverhult (1968-early '80s?) being real strong. The quartet variant that cut Fly Me To The Sun (Torbjörn Hultcrantz, Leif Wennerstrom) was really something; there are also two strong LPs on Amigo (one adding Bobo Stenson) and half of an LP for Sveriges Radio - the latter a pretty monstrous performance.
I've spent less time with the big band work than I should, but can recommend First Moves (EMI Odeon LP) as a knottily robust and rhythmically charged date. I still would rather hear him in a small group or, if in an orchestral setting, under someone else's direction.
Sideman work: In addition to some earlier sessions with Krzyzstof Komeda (who I have explored less than I should), Maffy Falay & Sevda rules as far as "non-Western jazz" goes, in my opinion, and the first of two volumes on Caprice has some killer Rosengren in that context.
Rosengren also worked with Don Cherry pretty frequently; the fruits of that can be heard on Improvisationer (scarce LP on SJR) and Movement Incorporated, a big band date released on the small Stockholm label Anagram (CD only). Orangutang!, led by saxophonist/arranger Gunnar Lindquist, is an excellent Cherry-inspired workshop big band date that's rare (Odeon Swe LP) but worth seeking out. George Russell was also seemingly quite integral to Rosengren's evolution as a player/composer and the saxophonist is on a number of Russell's Scandinavian sessions.
I recently picked up a Harvest LP under Benny Bailey's name that has some very strong Rosengren playing. It's titled How Deep Can You Go?. At times he sounds like Joe Henderson on that record, though I wouldn't say he always does. He's a robust player who amalgamated a highly structured form of post-bop improvising into relatively free (to very free) contexts and was successful at it. Clearly Rosengren was more comfortable with a somewhat regimented harmonic environment as his later records are more "in" than "out."