OK, the old Michelin Muds aside: I found several NOS 'cross tires hanging up at a shop in a small town and they looked like they'd be pretty good mudd/loose conditions tires but maybe I'm overlooking something.
IRC V-Cross: found one. Yes it's labelled as 700 x 37 but the casing is closer to a 33 or 34. Big, tall knobs with plenty of spacing in between. May have some rolling resistance on pavement/grass but looks like it will have some real bite.
Trek Matrix Multi-Track: found one. Labelled as a 35 but may be a bit skinnier. I found one person who thought these were like gold but no other references to them. Knobs very similiar to the V-Cross above. Looks to be another good mud tire.
Vredestein Campos. I no longer have but wish I did. The set I had I used up as a general off-road trail tire. Casing made the ride feel so smooth (to my untrained rear). Somebody hording these?