
You will find white mushrooms in almost every supermarket. Chestnut mushrooms, oyster mushrooms and shiitake are also more widely available now. Mushrooms are sold fresh, pre-sliced, preserved in cans or jars, and even frozen. When you buy fresh mushrooms, a bit of topsoil may have been left in the box, but you can easily brush that off. The other types of mushrooms available in shops should also be nice and unbroken, and should not smell like anything but mushrooms.
More exotic species, like the almond mushroom, are generally only available from speciality greengrocers and markets. High-end supermarkets sometimes carry them around the holidays, to add a festive touch to holiday meals.