Have you tried Acklands Grainger? Guaranteed they will have it... Might be a special order though
https://www.acklandsgrainger.com/AGI...130916040822:s
Princess Auto/Napa/Auto Value/etc... will often keep that sort of thing in stock as well.
And use a grinder bench, if in a pinch.
You can also get "cone wrenches" at any mountain bike store. They come in a variety of sizes and are 2 mm thick. If that isn't narrow enough... I don't know what else.
Good luck.