Did you actually look at that site? They state that most 650b tire are produced for the US market. Just because there is an enthusiast website doesn't mean that the tires are actually widely available. I kust searched four of the biggest European online bike shops and none had 650b tires. I did find a whopping TWO tires in the UK, one NOS for $65 a tire.......
Take a look at the site you linked to.....
http://www.confreriedes650.org/eng-tires.php