The way things have been, you have to check everywhere whenever you can. You will find powder here, primers there, bullets at another stop ect....Buy what you can when you see it. I looked for many months before finding one particular powder I needed.
+1
I keep a list of my supplies on my phone. Whenever I am near one of my reloading shops I will stop in and have a look using the phone for reference. Availability seems to be getting better thankfully.