I got them at the Dollar Tree. They have round ones and square ones and rectangular ones. The store I go to has white ones, blue ones or pink ones. I tend to get blue for boys and pink for girls. They make good water bowls for snakes too lol.

Edit to say I buy all sorts of things from the Dollar Tree to use for my animals. I use a lot of their boxes baskets and pots as hides for my animals. I am careful not to get anything that might harm the animal though. Such as the fake vines I've used in my snakes cages before. I had to go through and make sure no wires were sticking out or no sharp edges. I also had to hot glue some of the leaves to make sure they didn't fall off.
Last Easter they had a lot of baskets and I bought some plastic ones to use as hides for my snakes. They are now the only hides the snakes will use!