I just did an ebay search under model trains for dumpsters and got 22 listings under O scale. One of the listings is for the Artista dumpsters I have. 4 sides and two lids glued together. No bottom. I left one lid open and made "garbage" from a broken piece of Styrofoam painted different colors and pushed up through the open bottom.
And you can always check Shapeways the 3D printing website.