William Larkin Moore in Scottsdale, just off the 101, is worth a visit and they stock 2 1/2" 7/8 oz. 12g, usually 7s and 8s. I've got 2 boxes of 8s if for some reason they are out.
http://williamlarkinmoore.com/

Mearns numbers remain down, and it would be extraordinary to need more than 50 shells unless you'll be hunting for a week or with Bill Henry and Gil smile