Oldowan is a type of stone tool, not a specific set of artefacts. There are many thousands of examples of it around the world, and we don't have dating techniques precise enough to say which one of them is the absolute oldest. If you're thinking about the tools from Olduvai Gorge, which the Oldowan was named after, there's quite a lot of them and they're spread across a number of collections. I just checked and we even have a dozen or so downstairs in the building I'm writing this in. If you can get to a major national museum (e.g. the British Museum, the Smithsonian) there's a good chance you can see one there. Or I do know that they're part of the BM's touring exhibition, "A History of the World in 100 Objects", so you could see if they're coming near to you. But again they're not necessarily the oldest example of Oldowan tools.

Besides, the Oldowan no longer has the title of the oldest stone tool industry. 3.3 million year-old stone tools were recently discovered at Lomekwi 3 in Kenya, predating the Oldowan by a good half a million years. As far as I know they're still being analysed and aren't yet on public display.