You could try here for some starts:
http://www.youtube.com/watch?v=yfS1LBHBr8A
And I don't have the link handy, but there's a Bishop and Coulston drawing of at least one of them. I'm presuming you mean the pyramidal collet that goes around the end of the shaft/top of the tang? The gidget that keeps the wood from splitting.
I am setting up my forge soon in a shelter, and plan to make some of them, too. My idea is to draw a point on the tang end about as long as the tang, fold that back over, and forge weld it to the square stock. That will give from 1 thickness at the point to 2 thicknesses at the fold. More metal, thicker tang. Otherwise, the tang gets pretty thin, and is weak at the junction of wood and metal. Does that make sense? We know the Romans could forge weld. That's the only kind of welding there was in those days.
Let us see what you do. Everybody is always interested in people's metal work.
Also, I'm making a metal tool shaped just like the wood pyramid, and will heat up square tube red hot, then drive the tool into the hole. That will be the easiest way to get the shape right, I think. Quench, cutoff, done.
M. Demetrius Abicio
(David Wills)
Saepe veritas est dura.