You might check these guys out. I've only ordered minor stuff, but they list parts back to 1950. You can post a "request for parts" on their homepage. My understanding is they bought up a lot of Triumph Dealer parts inventory back when the company suffered financial indigestion

http://www.baxtercycle.com/

Good luck

"It's not what I say that's important, it's what you hear" Red Auerbach