Where to buy dried mushroom stalks?

I’m trying to make vegan mutton, and I cannot for the life of me find dried mushroom stalks. Whole dried mushrooms are of course no problem, but that’s not a very economical way to go.

A few Asian stores here sell frozen vegan mutton made with what appears to be just white mushroom stalks. I’ve also seen recipes that call for it, but I can’t find it for sale here in the SF Bay Area, nor online… :unamused:

Anybody know where to get this? I’d be willing to buy it in bulk if the price/quality is right.