Guncollector,
Yes, it was available with the Hornet (and still is, I believe). For years the Springfield catalogs also listed a 22 mag option, but I never heard of one actually making it to a gun store.
I'm thinking of buying another M6, this time with the new stock/trigger configuration, the 22 Hornet barrel, and the rifled 410 barrel that is supposed to handle 45 LC rounds. However, I'll probably still use the 22/410 more often. That 22 is awfully handy for popping grouse, ptarmigan, and bunnies.
My first target with the M6 got mailed to Springfield with a thank you note. After a fouling shot, it put five rounds in about a one inch hole at 50 yds. (off a bench). Hard to believe with a short bare barrel, fairly primitive sights, and a funky trigger mechanism. It will shoot minute-of-bunny at 100 yds, but I've never needed to try that long of a shot.