In college I had a book which described how to do Celtic art, from the knotwork to the mythical beasts. I used a lathe to turn the basic form, then worked from there. There were several books with different dirk styles I pored over. I was lucky as well, in that I had a friend with an antique dirk, so I could see how it was laid out as well. I got pretty good at it, but really didn't follow up what with a family and all. But I still use the procedures to lay out lines to carve on the bits I do now for fun.

Vince Evans does fantastic work. Apparently he does have a book on carving dirks (I just found that out). Google "Evans Scottish dirk".