You can buy them , but it's easy to make one . You need a shallow plastic box with a lid , a kitchen sponge and wet pallet paper . You can get the paper from art shops , but I see that some use parchment paper which is available at the grocery store . Add enough water to the box to get the sponge really wet . Put the paper on it making sure the paper gets wet but not soaked . Use the paper to put your paint on and to mix . The damp paper will prevent drying out and if you put the lid on it will stay good for a day or 2 .I have not, I heard about them but have never tried it. How's it done?