"Hey, great organisation/research on the 650B world. One Q that's irritating the F out of me: (why) is nobody out there making a cx type 650B tire in the 35-42C range that can actually handle real trails and fit into road frames? For a do-it-all practical bike, I have my old road frame-city bike that I ride all snowy winter with beautiful jaunts into the trails but have tiny 25c cx tires on it. Any tire like this hiding somewhere out there?"
I'd like to think that I have all of the decent 650B tires listed to the left. I think the tire you're looking for is not yet produced. The folks over at Pacenti Cycle Designs has some tire designs and I believe they have the Mini-Moto on the drawing board. I too would love to see a tire similar to what you desire, and I'd put money down to say we're aren't the only two.
If you'd like to ride a more fledgling tire size in 650A, aka 26 x 1 3/8", Kenda offers a knobbie tire close to the range you mentioned. I know it is available from USA distributor SBS. While 650B has a bead seat diameter of 584, the 650A is at 590. SO, this elusive tire will not fit a true 650B.