I was at the Big R in Michigan City yesterday. They had shelves full of shotgun ammo. They did however have a sign posted at the entrance to the store of a limit of two boxes of ammo per person per day.
Shotgun ammo doesn't appear to be part of the panic. It is still widely available just about everywhere. I think prices have increased just slightly in the past year or so on shotshells.
I will say that 00 buck seems to be more difficult to locate than slugs and birdshot.
No issues around here for shotgun ammo. I bought a few boxes of 12ga #6 a few weeks ago and have been seeing them at Walmart, Meijer, and Rural King pretty regularly.
I'll have to agree with everyone here. Bought a Mossy a few weeks ago. Went to Wally World and picked up their last box of .00. Bought their last box of 100 8's. But there was several box's of 100 7.5's. To the OP, the 100 boxes aren't stocked behind the counter. They keep those but the targets and clays.