Hey Channing,
Assuming you have a handle mechanism or 5 already, my guess would be to look online at the different manufacturers and order the woody blanks from them or their preferred supplier.
First Prize: If you can find one that matched the brand of handle you have.
Second Prize: You might have to modify the timber barrel to suit, provided it doesn't compromise the strength of the joint.
I am considering making my own in the near future. I am pretty good with timber, so it might become a hobby when Conditions are gross.
Hope you come right mate.
Cheers,
L
