The issue of powder and primer shortages is primarily a function of the supply chain--not really import laws, although it seems that the problem is a little more acute here in Canada than in the US. They are having many of the same supply problems in the US, but the thinking is that US suppliers are exporting less than usual to Canada--keeping more than usual in the US because of the market size.
The supply problem has many causes. Supply of the raw materials is way down. Manufacturing is way down, with many manufacturers having laid off workers because of Covid and their own supply problems. And then the shippers are hamstrung too with labor shortages owing to Covid and less product to ship. The consensus seems to be that more product is being diverted to fill military contracts than usual, leaving less for the civilian market, and a lot of the components which are not going to the military market, are being scooped up by the ammunition makers rather than being made available to reloaders. This is all happening in the US, and then to top it off, we in Canada are at the end of the supply chain, with the a larger proportion of product than usual staying in the US.
Another factor is greatly increased demand by shooters in the US. Evidently, the number of new shooters and reloaders has skyrocketed with the change of government in the US--from a conservative to a liberal White House and senate. So supply is down and demand is way up. A perfect storm!
About the best advice I can give is to be relentless in your searches. Check all the online sources regularly, and, if they are out of stock (as almost all of them are right now), leave your email to be notified when they get the product in that you need. Most online sellers provide this option. I've done this with many online sources, and out of the blue a few weeks ago, I got a call from an online store telling me that the powder that I had asked for notification about had come in, and they could supply it to me. To be honest I was shocked (and happy!), so it pays to stay in touch with suppliers. Check the EE here on CGN regularly, and check ####### and Townpost.
Best of luck in your searches.