I can't help you for those specific powders at the moment. (sold out everywhere I think).
I recommend using multiple strategies:
1) Local gunshop: I used to get powder special orders done at my local gun shop. They knew if I did not pick it up when it arrived, that they would sell it fast anyway, so no risk to them. The shipment was not really just for me, it was for the store. But it got my name on a list for first dibs for the amount I wanted, when their shipment arrived, and they would call me on the phone when it arrived. Relationships with local gun shops are well worth cultivating.
2) For the online stores: I have my favourite store websites that I watch just about every day. Powder may only be in stock for a day or two. You have to be fast.
3) For the online stores: Become a customer and sign up for their newsletter notifications thing. Get on their database. You may get first notice of pre-orders, and heads up on when new shipments are incoming. I got my N555 on just such a pre-order notification. Had to wait several months for it to arrive, but it was worth it, and I bought several containers.
4) When you find a powder that works, buy in bulk (e.g. 8 pounds, or several 1kg containers), because it can be a year or more before it is available again. The dangerous goods shipping fee may be the same regardless of amount, making it cost effective. For example, online I recently bought 3 kg of Vihtavuori powder from a CGN vendor sponsor, along with 3 bricks of rimfire ammo, and 1000 projectiles. Very heavy box! Shipping was only $44, which was dirt cheap.
Best wishes for finding your components. Hoping for better supply times ahead.