The closest to correct size is 185/80r13 so i would be looking for that size.

Maxxis m1a is the most commercially available. Best prices are usually found on line. My local les schwab could order them so you might want to check there.

Expect to pay around a $100 a tire though. The days of cheap tires are long gone.. between the crack down on tires made over seas and the elimination of the smaller tire sizes have driven prices up.