Sorry for the ridiculously huge bump, but if my memory serves correctly the Tristan knife was made by Daniel Winkler. I can't find the magazine at the moment, but I did have an article from Blade magazine that stated that Winkler made the knife for Pitt's character in Legend's of the Fall. It also goes on to say that Pitt purchased a knife for each of the actor's/actresses involved in Legends of the Fall.
Hopefully, I'll be able to find the article before too long and get some scans/photos of the article.
Great site by the way!