Originally Posted by
Gresp15C
...someday I'll need new tires and will discover that 27" are no longer available...
You won't live that long.
I keep reading about the death of 27" (ISO630) [and now 26" (ISO559)!] tires. You can still buy ISO597s, guys and gals, and that size tire hasn't come on a new bike since the 1950s (and wasn't even common then). At least until a few years ago (and maybe still?), you could buy single tube tires and they've been obsolete since the early 1930s.
27s are widely available in discount brands. Fine quality 27" German and Japanese tires are available from Schwalbe, Continental and Panasonic. Specialized and Trek (Bontrager) both catalog 27s. Your LBS doesn't stock any 27s? Well, you gave the local cats a shot at your business. Now have some delivered to your house tomorrow from Amazon.