A common misconception among many pipers, especially newcomers, is that stems are disposable. Plug and play, one size fits all, etc. Truth be told nearly all pipe stems are custom fitted for its own individual pipe. On normal tenons, a diameter difference of 2-5 100ths of an inch can make the stem too tight or too loose.
In your case, the military mount makes things slightly easier, but only slightly! In my experience an adequate stem replacement can be had for around $25, but the wait for those who charge that is long. You could try yourself, but it would be a risk because you don't know if the angle of the tenon on the replacement stem will match your mortise. Pipe Maker's Emporium has several in that style for $7.50 each.
Might be a fun project, or a waste of money. Good luck in your endeavor!