I wanted to but couldn't find one so I used the regular type. I imagine it would last forever though.
I don't know how many miles were on my plug, but it had to be 8,000 miles. It had no insulator pitting, the gap never changed that I could gauge, and it had no visible electrode wear. I really don't know why I even changed it.
God. Family. Motorcycles. Guns. Music. Books. Dogs. Beer. Baseball. Work. That about covers it.