My wife lives in a small village in Ampher Cham Ni and there's hundreds of mushroom farms all over the place. To find one, all you have to do is wind down your car window, turn off the air-con and follow the smell (chicken shit). Or if that's too hard, keep the windows closed and the air-con switched on and follow the flies (lovely). These mushroom farms are illegal if they are in a village; however, as with all good back handers people are starting these farms all over the place.
Please look into this carefully before you start as the smell and the flies are intollerable. As far as I can see the only people who start these projects are the very poor, who have no other choice.
Good luck, but don't say you haven't been warned.
Andy.