Where to purchase large containers.

For many years, I grew my garden in fifteen gallon tubs. Now for many years, I've grown everything in raised beds. Two years ago, I started adding some containers back to my garden, but have experienced difficulty locating a supplier of the larger (ten gallon or larger) nursery tree pots in the black plastic. Everyone seems to be selling highly decorative pots at high prices and I only want functional, not decorative. Any suggestions?

Ted