Any bike shop that deals with QBP (most) can get you a 650b wheel/tire as well as Velo-Orange, Riv Bikes, and a few others. While I concede that you can't walk in most shops and buy a 650b tire off the shelf (again 26" tubes work fine), you can get them pretty quick by mail. As far as it being an inconvienence...how many people only have one bike to ride if they blow thier 650b tire? As far as on a tour, a folded kevlar beaded tire doesn't take much room....
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If you have a problem, if no one else can help, and if you can find them, maybe you can hire the A-Team.