Hi Bruce,
The kit that I made my filer from is available here:
Our kits consist of castings, drawings, and machining instructions
It's more of a "Cadillac" version than most people really need.
Martin Model sells two "open" versions, though the basic price is roughly the same:
All Martin Model gray iron castings are fully annealed for ease in machining.
The Metal Lathe Accessories version has several added-cost upgrades which push the price up considerably.
Here's a short video of a guy using the Metal Lathe Accessories version to file a square hole in a gear:
Also, here is an animation of a half-section of the MLA die filer I made in Solid Edge
Paula