“but also in dried form in powder and capsule form, from health food stores.”
Works great at reducing the weight and bulge of you wallet.
Grow your own. Everything is better as God made it. Field and Forest is one of the best suppliers. Commercial growers use them.
https://www.fieldforest.net/category/lions-mane-mushroom-spawn
I’ve grown shiitake outdoors on oak logs. Lion’s Mane are a little more finicky but they sell kits for different, easier methods than outdoor log growing. I live in a oak/hickory area and oak is preferred for shiitake.
I don’t have Beech, Sugar Maple or Ironwood which is the preferred substrate for lion’s mane so I would go with a ready to fruit tabletop kit for myself.