The AC M-8 plugs are listed on the Auto Zone website- - - -with free 2-day shipping. It doesn't seem to be much of a problem getting them online if your local store doesn't keep 'em in stock. A 15-second Yahoo search turned up several sources, including the one I just quoted. Yes, they have a 10MM thread.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!