Drop-ship suppliers will usually supply you images of their products, quite unusual if they don't. What some people do is buy one of everything that are going to sell upfront. This allows them to test the quality first, but also to take their own pics as well, so that's an option if you wanted to do it that way also.
If for some bizarre reason the supplier won't provide images, well I think I would seriously question if they are worth dealing with firstly. If you still wanted to go ahead, then do a stock Google search and see if you can find images there that are suitable for manipulation.