While I cannot speak from experience, 700c is an international production standard.
27" was generally only a US standard and is now obsolete for OEM the most part.
650B, 29 and 27 1/2 labeld tires might be a bit more difficult to find.
It would be hard to believe that any bicycle retailer would not stock or have access
to tires and tubes of that size. Even big box type stores.