I've got around 10kg of them from a couple of trees in my garden. I've done zero maintenance, they're just there to keep other shit from growing (walnut trees poison the soil, most weeds stop growing, also because of the shade). All "high quality", the same stuff you get in stores.

Walnut trees are used on roadsides, they're perfect for it, zero maintenance, keeps the soil from moving/sliding and kills weeds. Random people just harvest them if they want to.

The store prices on them make no sense. Just like bananas :D