The stores around here still stock 16 gauge ammo, though not in the quantity or variety of 12 or 20 gauge. As zippy said, it's all about the market. The 16 gauge has been said to be dead since I started shotgunning in 1965, yet it continues to hang on, primarily from all the old shotguns left in closets and gun safes.
My Dad shot exactly one shotgun, a 16 gauge Model 12, all his life. He shot everything with it, from rabbits to geese and it served him well. That shotgun lives at my son's house now.
