Remember - tire manufacturing, like swimsuits and ski gear, is season dependent. There are so many types and sizes of tires that manufacturers plan a run to make sure they have the right tires for the peak of demand. So, winter tires are typically sold out in the spring and summer tires are sold out in the fall. Off road tires are usually sold out until spring, no matter where you live.
Except this is all tires. And it's been going on for more than just the fall.
In case you haven't noticed there's an issue with most products. New cars. Food. Electronics. Try and buy a gear set for an 80 series land cruiser.
Go to the store and find 15w40 oil. In any brand.