Originally Posted by
icepick_trotsky
Many older bikes like yours came in 27 inch, which is very slightly larger. This size is now obsolete
Hmmm... I don't think we need to start a semantic battle here, but that word has connotations that are misleading. Lets just say there is a HUGE worldwide stockpile of everything 27" related and that's why dozens of tire manufacturers still gladly make a wide range of tires for that size of rim. They will be marked, as an example, 630/32 or (27" x 1 1/4") for one very popular size, available from dozens of manufacturers. A 27" x 1 1/8" tire is also known as a 630/28 and a 27" x 1" is a 630/25, etc. as the tires get narrower.
The nomenclature is admittedly a bit confusing, but the tires themselves are easily found.