Check out - River Valley Mushroom Farm - Burlington, Wisconsin. Located 39900 60th Street - which is the intersection of (highway 50 & P) in burlington - new munster area.
They grow a variety of mushrooms and ship world-wide & are Closed only one day out of the year. I believe they have a website - but not sure of name (try a search).
Also the store is filled with gourmet selections of homemade pickled, garlic, jarred mushrooms, Salsa's, home-made soups, chocolates, gift packages, fresh fruits & veggie market and more.
If you get a chance to visit the store - they have taste samples of everything ( it takes about a half hour to try everything)!!! ENJOY
They also sell (for the green thumb) a mushroom compost * your garden will luv U*
Its a hike from downtown, but H-Mart in Niles has a huge produce selection. You could certainly find asian style mushrooms (shitake, enoki, etc) but they have a very diverse selection there. At any rate, a very interesting place to visit if you have never been there.
I have seen these at Whole Foods as well, ableit at their typical high markup.