i'm pretty sure triumph makes a solo seat. they did a "Thunderbird Sport" with basically the same makeover they've done to the Bonneville \ Thruxton....a factory cafe. so the seat should be around.
one of the coolest modern cafes i've seen was down in NC. the guy took a creamcycle orange Thunderbird, added a Speed Triple front end, with clip-ons and all, resevoir shocks, mag wheels, hugger, etc....very hot. i dig the triples.
The Thunderbird Sport has a different subframe than the standard 'Bird, so the seats won't swap without some modification. I had the same idea for mine several yrs ago, but I have kids who want rides...
I'm sorta looking for a spare stock seat to modify for my '95.
mecatwin has a site with english translation....their stuff is hot. sometimes it flips back to francais, just click the english button again. i have a modern bonneville and have used some of their gear.
speaking of which, the AMA just added another date to the flattrack schedule...Monticello Raceway in Monticello, NY on Sept 15. it's a pea-gravel horse racing track, and only 'bout 45 miles up Rt.17 from Westtown. i kinda know a guy that's developed a mondern bonneville to go against the HDs and will be running a full season this year.