Submitted by Alan
Nite Ize (niteize.com) makes at least one push-button tailcap for AA Maglites, along with 1-watt LED upgrades.
REI carries a combo of the "IQ switch" and LED (item 760026) for $20:
Note that the IQ switch might not be suitable for military use; it includes a low-power blinking LED in the replacement tailcap. I didn't see a non-illuminated alternative on their website.
ED -- Alan, Thanks for the info. Items # 737322 and 743038 from the REI catalog appear to be Nite Ize products, and given the numerous products Nite Ize offers, I'd seriously recommend skipping the middleman and going straight to them for your maglite upgrades.