Powder valley has had a lot of powder lately and they have been putting them up at all different times of day and amounts. it is my belief they are doing that to help control the attack mob. I even seen powder show up on sundays
If you're after one thing specific open a tab up for it on your phone and refresh it every time you use your phone. Not perfect, but you only need to get lucky once. I'd you're after a bunch of stuff, sometimes they post on Facebook that they got a shipment going up later today.
I have 5 websites that sell powder open on my phone that I refresh many! Times a day. I got lucky last month and got some blc2. It's like playing a slot machine at this point. Just hoping that I hit 3 cherries at some point.