<img src="images/graemlins/confused.gif" alt="" />***Maybe I am missing something here, but couldn't you just buy a Mag Solitare and strip all of the guts out of it?  ****   
Where's the fun in that? <img src="images/graemlins/grin.gif" alt="" />
Actually I was thinking just that with a mini-Mag  sized light.  Remove the head, seal the end with a disk of cardboard, and apply a nice thick coat of JBWeld over the end and threads.  After it dries it can be sanded smooth no sweat.  It might not look as cool as a fancy, machined plug, but it should serve just as  well unless you really have to have access from both ends.
Ed