I have a questiong where can I find mushrooms?

Mushrooms seem to sprout anywhere a seed might spawn in the world. If you're playing Moonlight Falls, there are also mushrooms pre-planted on many residential and community lots (for instance, check the "treehouse" lot where the mischievous fairy family lives, or the house with the adoptive mother and her changeling fairy child).

At night, the "spotlight" mushroom is pretty easy to see from the map view.

Mushrooms can also be purchased at the new elixir consignment shop (and possibly the grocery??).

I am playing Lucky Palms and the darn things are everywhere, most are in the dried lake beds. Try the playable edges of the world too.

Where can I find the treehouse lot?

Some of the mushrooms (the porcini and white specifically) can be purchased at the grocery store. There are occasionally other types at the Alchemy store and over by the Gypsy Caravan in Moonlight Falls, there are several types of mushrooms growing. Also, at the Alchemy store in the back "yard" there are several types of mushrooms back there. I've also found a few types at Fae Ray's Gardens, where the Arboretum (sp?) is located. You can also find Life Fruit there.

And you can find mushroom spawners in buydebug, if you want to cheat and place your own

BTW, like any spawner, mushrooms will take a while to appear and mature to where they're pickable in a new game... so if you've just started, I'd wait a few days for mushroom hunting.

The fairies live just below the Stone Troll fishing hole, IIRC.