Hi,
I know of two companies that have offered T300 steering damper kits, and I think they were born out of the Speed Triple Cup. You may like to take a look at the following old post:
http://www.triumphrat.net/t3-sport-t...ed-triple.html
Although produced for the Speed Triple, I suspect the kit will work on all the Thunderbird models, etc....
I guess you are interested in this because you like the look, or because your TBS is highly modified? The standard Thunderbirds models are very stable machines normally.
Hope this helps?
Geoff