I carry an extra tire, due to having ripped one up once. I can't see going through more than one very often on a 720 type trip. Did you look into getting a different fork , normally you can jab some tire width into the back.

Actually, The reason I carry a spare 700 is because I blew one, came into a nice little town, with a really good repair shop, still no 700c touring tire. I got a soft comfort bike tire, the type that de-rims at 60 pounds. That got me to the provincial capital, with a large university, etc... And some very tasty bike shops. Still no 700c touring tires, so basically I don't think there is any much greater risk in going 650b than 700c, you are on your own with either.

Toronto were I live is the 4th largest city in US Canada. You can have trouble finding basic touring gear here. It is to the point where I don't even bother looking, I order everything from the US, and to do that efficiently I give myself 6 months lead time. If you were in need, you could get tires in most of the large cities at an MEC, but if they don't have what you want, and they rarely have the stuff I want, then you are down to calling myriad small stores, some of which are very good on touring, but do not have any specific item you want. I once couldn't find a touring cassette anywhere, they had lots of 26 inch wheel specific choices but nothing for a 700c bike. And everything cost twice as much, depending on where the dollar is. I would guess there is a somewhat similar issue in many parts of the US, not on mail order, that is awesome. But the fact mail order is awesome means local shops are out of the loop often, and one hears lots of stories of people who can't find any touring bike to actually try. I never rode any of my touring bikes before I bought them.