As Rick mentioned, both Lowes and HD have metric bins in their hardware aisle. They are separated from all the imperial hardware and much smaller in variety and quantity, but you may find it there. Biggest issue I've had is nobody seems to pay attention to stock or organization there, so if they have a bin for the specific thing I need, it's empty or has some other part sitting in it. More often than not, it's proven to be a waste of my time and gas. I'd check with Festool or McMaster. Either can get it to you quickly and the shipping expense saves you the time you would have spent grumbling at the big box store.