Local hardware store, in my case it was a True Value. It's M6 x 1.0 thread pitch, stainless. Take the old one with you and get an approximate length. It need not be exact and can be longer than what was in the frame. Long enough to fit through all the threads. For example, if yours was say 22mm, get a 25mm replacement. They'll likely have the same stock most every hardware store has, and they come in 5-10mm incriements. They also have the locking nylon-infused nuts if you need one. Make sure to grease the new bolt threads upon installing.
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