drill, tap, buy some bolts and a number bit set and you can make yer own. Thats all the Mccann gas plug for the Garand is. 8-32 allen head cap screws with various size holes. No lathe required, you could do it at the kitchen table
be sure to post pics, M14 handloaders can really benefit from this for heavy loads
Doesn't Dlask arms have something like this that allows you to change the timing of you piston? Is this not the same?