I have bought several woody plants over the past few years that come in what I have been told are called 'bands'. They are black plastic pots that are generally tall and relatively narrow, ostensibly to develop a longer root system. I have saved the pots that I have gotten but would like to find them in bulk for my own propagation. Some of these pots are about 2.5" wide x about 5" tall, and some look about 3" wide x 6 or 7" tall.

I have been searching online in vain. Can anyone direct me to a supplier that carries this type of container? I have found cardboard-type bands but don't want those; I want to be able to bury the bands in nursery beds to root dormant wood cuttings over the winter. Any help is appreciated.