Frame USA offer Wholesale Picture Frames For Artists, Museums & Home Decor. Smaller sizes for desk or table displays as well as flat backs and larger sizes for wall mounted ready-made frames. Frame USA have a frame type for every style or decor. Wholesale picture frames are available in wood, metal, acrylic and plastic.
https://www.frameusa.com/wholesale-picture-frames
note from editor: I have used Frame USA as a source for frames and personally can recommend them.