Tires for a 66 Dodge Dart 270 Convertible

I need new tires. Currently I have 185/80 R13's on my Dart. My tire shop cannot find any tires of that size. Please let me know what other size tires I could use. FYI, I have owned the car since 1974 and my original slant six engine has 299,300 miles on it. This is not a show car, I drive it about 2000 miles a summer around town.