We all buy these. Sometimes, at great expense (see Truffle Salt.) This is all easy as fuck to make at home. Got some salt? A flavor you want to mix with salt? A way to dry it all out? Ok, you are in business. Do this:
Take your (peeled) garlic, your (greenest parts) celery or fennel or super-fine chopped herb like rosemary or dill and pulverize it into nothingness in your food processor. Then mix in a bowl with kosher salt, blending with your hands or a spoon until it looks like it is about half salt and about half herbs. It’ll be chunky-wet and unmistakeably green.
Spread out 1/4″ thick onto trays in your dehydrator or cookie sheets on the lowest heat (160F) in the oven until dry, 4-8 hours. Break up with hands every 2 hours. Grind again in food processor after dry if chunks are too big. You are welcome.