Unfortunately, Walter Cain passed away a few years back. You might try Tip Curtis (615-654-4445). I remember seeing one of Mr. Cains single lever, double set triggers in one of his display cases on my last visit to Friendship, but I can't say if he had any Hawken Triggers. Your best bet is probably going to be to advertise your need in the "Items For Sale/Wanted" section of the ALR site (just remember to state how much you are willing to pay). His finely crafted triggers and assembled locks command high prices these days, so guys that have them won't let them go cheap.
Earlier this year, someone posted a Large Siler lock assembled by Walter Cain for sale here on ALR. This was one of the rare times I scored something I really wanted before it got scarfed up 8 minutes after it was posted! I also have two sets of Mr. Cain's single lever, double set triggers: one in a rifle (kit) I bought from Homer Dangler just after he sold his kit business to Jim Klien, and another set aside for a future build. If you find the set you're looking for, bite the bullet and buy it. Good luck in your search!