You can find powdered seaweeds here: https://naturespiritherbs.com/

Powdered herbs here: https://mountainroseherbs.com/

And powdered vegetables and herb blends here: https://www.drcowansgarden.com/collections/vegetable-powders

And of course you can always make your own with a good dehydrator (dry herbs anywhere from 95-115 degrees for a few hours or until dry and crispy) and then use a blender (let the powder settle before you open the top or you'll have a cloud of *whatever* wafting throughout your kitchen).