26 x 1 3/8" is actually the tyre size you need. It's an old size and emphatically NOT the same as 26 x (any decimal fraction).
The tyre will have an ETRTO diameter on it somewhere. The rim might not, if it's old. Is it an American bike (going on your spelling of "tire")? Almost uniquely, 26 x 1 3/8" can be one of two ETRTO sizes. On a British bike it is 590mm but on a US bike it may be 597mm.