Check these out...
http://stores.ebay.co.uk/wonderful-market2007
Now, note that these are Nylon/polyester copies, not waxed cotton, but much cheaper. The photos are a little decieving. Also note that these would probably be OK for spring and Fall, but I'd be careful about winter wear. No, I haven't ordered from these guys, but I'm seriously thinking about it.
British Motorcycle Gear is the Belstaff distributor in the USA. I talked to these guys at the Chicago Cycle World Motorcycle Show this past February, and they said there are no more Trialmasters to be made. I have a Belstaff Mercury Jacket, and it's absolutely great. Fantastic quality, fit, very nice work. BMC is also very nice to deal with. The first jacket was a litle tight, so they sent me the next size bigger, before I even had a chance to return the first one. Rare in this day and age.
Lot's of the old waxed cotton ones on ebay, or try this canvas one as well:
http://www.johnsonmotorsinc.com/men/isdt2.htm
Note that there is no protective armor in these jackets.