I was able to buy a 333 round box at wally-world last week, it was one of two boxes and the guy before bought the other box. I think it was $9.95. Anytime you go to a PA WM, check out the ammo section, they may or may not have any.
Almost a month ago, I was teaching at a Scout Camp, over the course of three days, emptied three WMs of 20ga birdshot and all of their clays.
It looks like demand is just too high for production to keep up, for now.