But gee Mimi, once you get the 650b rims you are set with that. As to tires...well tires you just get on the internet with a click of a button- you don't have go traveling around looking for various 650B tires in bike shops. Most shops just carry top selling stuff anyway.
The 650b's are even more limited than the 650c's, though! You can't get those any smaller than 30mm, not in the U.S. I really wish that, instead of pushing these two wheel sizes separately, bike manufacturers would get together and push for the availability of a wider range of tire sizes in one or the other. Wouldn't that make so much more sense?

The LBS I frequent carries what people want. They carry 27" stuff even though that's an outdated wheel size that is not used on any current bike that I know of, because they have enough customers with older bikes to support them keeping some of those tires in stock. But even though they sell a lot of women's bikes, including some with 650c wheels, they don't even have tubes in stock for 650b tires. That would drive me insane, not being able to buy a tube locally.