The sentiment is appealing, but folks have been stocking up on guns and ammo for the past couple of years. The problem with a national buy ammo day is that the stores will be cleaned out - they can't stock enough at one time. Better to continue as we have been - buy what you can as you can. That gets you where you need to be, and helps the stores to keep plenty on hand for everyone.
I just received a $1000 dollar shipment of ammo for my gun store Friday (I know, $1000 isn't a lot, but my store is small) - don't know how long it will last on the shelves, but I'll stock more as it gets depleted. If you buy me out in one day, it takes 3-4 days to get another shipment, and my shelves are bare until it arrives.
Just my $0.02.