Just start making your own. It's actually really really easy.
Required equipment:
Big mixing bowl
Electric mixer
Required ingredients:
Extra thick double cream/whipping cream
Optional ingredients:
Salt
Garlic
Wild garlic
Insert herb here
Process:
place cream in bowl.
whip until it separates, folding the chunks back in and stop when there's only butter and
decant newly made buttermilk.
wash butter to remove buttermilk by filling bowl part way with cold water and just squeezing the butter. Switch water and wash until no visible milkyness comes out of the butter.
add extras by folding or blending it through the butter.
store any butter you're not likely to use within a few days in the freezer, I like to portion it out into 100g bits, so I know I won't be wasting any of it.
There, now you'll never have to wonder what your butter is made from again!
I would like to say that while this is clearly made in jest, unsalted butter is a requirement for some really great recipes, and also some people are on say a low sodium diet. I put it as optional, because I'm a mature person and don't yuck other people's yum.
Traditionally, salted butter was way saltier than our modern salted butter and it was a way to make it last longer before we had refrigeration and pasteurisation
When using butter as a spread it's nice to have some salt incorporated. A salt shaker is very easy to overdo on something light like toast or pancakes.
Unsalted butter should be used when cooking specifically because you can control the salt level yourself directly by... Adding salt. It's easy to add salt, but very difficult to rebalance a dish when something is too salty.
Salted butter should be used when you're adding it to something that's already done, like when buttering toast.