I can tell you about black powder sales in Wisconsin. My best friend owned a gun shop (fancy that). He carried all kinds of powders for reloading including black powder and Pyrodex RS (at the time, that was about it), you needed.
The State of Wisconsin, and Federal Government passed safety standards regarding the shipping and storing of powder by stores like his. His insurance company told him that in order to sell black powder he would be required to build a vault in his store. They even supplied him with the specifications of the vault, and it was going to have to be inspected by them when completed. Further, if he wanted to display his product on shelves, he had to return it to the safe each night. Now the sub powders do not fall under these requirements.
He priced the cost of the vault, figured the profit on his sales of black powder, and when the date of you had to be at these standards came, sold me a bunch at cost, and moved the rest of the powder to his house. Where there were no restrictions on its storage, but he could not sell it.
That is why it is almost impossible to purchase black powder in Wisconsin from the Mom and Pop stores. Some stores do have it. They don't tell anyone, but if you mention you need a pound and they know you, it suddenly appears you might say. Even those are about all dried up. That's why I buy mine by the case.