Can't quite figure out how to make a link to the site work (I'm a bit of a Luddite). I just did a search on e-bay this morning for "dirk blades". Came up with several knife listings in the auctions, and 3 blade listings in the "e-bay stores", all from "ancientarms_etcetera". That's the outfit that was mentioned earlier. I've bought their sgian dubh blades in the past, as well as some of their large dirk blades, the ones they list as "Big Sam".
I made them up with an eye towards using them at reenactments, but mostly wound up giving them out as prizes in the Highland Games that I run at some of the Rendezvous. Eventually I'll make myself a proper early style (mid 18th century) dirk, either at the forge or by stock removal from an existing blade.