No, Blue Ballads isn't listed on AMG for some reason. But it's on the Japanese Venus label, and is a very worthy listen I think. I think that Cadence might carry it.
Another really good one is Ginseng, a 1986 date made under the co-leadership of African pianist Tchangodei, about whom I know nothing other than that he plays really well. More info here: http://www.tchangodei.com/frameset-mus-gb.htm
The side on Fluid w/Joe Lee Wilson is called A Touch Of The Blues, and to my knowledge has never been out on CD. Worth the hunt, but it'll probably be a long one...
The Delmark side w/The Ethnic Heritage Ensemble is readily available, although I think it might be more readily appreciated by somebody who's followed Shepp's later years with interest rather than relative disinterest.
All the Steeplechase duet sides w/Parlan are very much to my liking. Also on Steeplechase is another duet album, this time with Jasper Van't Hof, Mama Rose, that I've always been fond of. It's got both sythesizers & Shepp vocals, so be forewarned, but the music has always reached me.
The duet sides w/Max Roach are truly essential latter-day Shepp, I think. The Long March on hat is the better known and more easily found, but another, significantly more obscure one, Force, on the Italian Base label, is the shit afaic. That bad boy is serious. But once again, good luck finding it...
Of course, no Shepp collection is complete w/o his performance w/a then unknown Whitney houston on a Material side, but that's edging into, shall we say, "esoterica".
Shepp's been such a whore about recording over the years (really, he was David Murray before David Murray was...) that you gotta wade through a whole lot of shit (ranging from merely mediocre to truly horrible) to find the good stuff, and quite often the good stuff is on little "rural" labels that came and went w/little more that a (hopefully) few coins for the players at the end of the session and a few LPs that made it out into the world for a few minutes. And other than the Steeplechase sides (with & w/o Parlan), I can't really say that any of Shepp's "high profile" (in terms of American distibution) dates have shown him at what I would consider his latter-day best. C'est la vie...
As for the tenor thing, yeah - it's a very physically demanding instrument, especially if you approach it like Shepp does/did and use a wide open mouthpiece, the stiffest possible reed, and an embrochure that basically consists of frequently swallowing the mouthpiece, blowing as hard as you can, and letting your cheeks puff out to an extent that rivals Dizzy Gillespie's. That's what he needed to to to get that powerful sound of his, but you can only taunt nature for so long, if you know what I mean...