One of the places that has been around for awhile that has a good selection of supplies AND kits (for the beginner up to the master smith) is the Texas Knife Maker's Supply store
Another place that looks good, although I have never dealt with them is the MidWest Knife Makers supply
I also came across a place to get a Sheffield's Supply Catalog on line.
And then there is always the Jantz Supply site.
I hope these prove to be useful to you.