I think that tyre was a Cheng Shin 3.25x19 (C186?) universal Firko. Availability seems almost 0 nowdays. I'm going to be hunting the same thing myself very soon although preferably a 3.50
Will post details here if I stumble onto more than 1 of anything in a half decent size
Thats the same casting as the dunlop trial universal even same sips and direction. But i cant find that pattern over 3.00 in a 19" would need 3.5 as a min, 4.00 same as the 4.00 x 18 they sell would be awsome. its not the C186 that no come in 19 and its a small front open tread.
the new speedways have a tall edge, but the older ones the tread comes over the side, maybe the an early speedway might have enough on the side knobs, but still may have th eissue with the walls and knob structure.
Keep looking, post if you turn somthign up..