My recipe for success in finding powder and primers...
Pull up a web page for several of your favorite vendors and your desired powders/primers.
Refresh those pages every few minutes.
When you see your stuff available, buy it RIGHT NOW. And buy a LOT. Buy enough that you won't have to do that again for several months or a year at least.
As I type this I'm seeing Unique, Bullseye, AA#2, AA#5, RedDot, HP-38 powders, CCI/Rem/Win/Fed small pistol primers all available. Powders range from $18-$28 per lb. Primers are $20-$31 per thousand. There's lots of other powders available that I don't use. Large pistol primers always seem to be more available than small but I don't use any large.
I buy primers at least 5000-10,000 at a time. 10k primers lasts me about six months.
The smallest amount of powder I typically buy is 2x 1 lb if I'm trying a new powder. If I can buy 2x 8lb (or more) of something I'm familiar with I buy that.
Buy in bulk, when the stuff is available at a price you like. Don't buy 1000 primers at a time. Don't buy 1lb powders if you can help it.
I do the same for motor oil and filters, laundry detergent, canned food, bars of soap, TP etc. It's not about "prepping for zombies", it's about not having to go to the store every few days AND it's about saving money buying in bulk when the price is right.
Sgt Lumpy