4380R...
Finding 13" tires these days are like hens teeth.
A true dilemma as most period radials have long since had their dot numbers expire. Only a hand full of companies are actively producing 13" rubber at the moment...and it ain't in the USA.
You can go the overseas route and pay thru the nose for shipping and the exchange rate, or pick your favorite Korean tire here. Depends what you want. If you want the traditional stagger of 175/185 try these web sites "Performance Plus", 10/10 tire, Coker...If you are intrested in more of a sport tire...Sasco Sports will have Avon & Goodyear made to order with Toyo and Yokohama available.
I recently purchased a set of Nexen 185/60's all around for the factory wheels, but the rear tires seem to get lost in the wheelarch. I also have a set of Yokohama 048's....the car has a much better look and rake with 185 front & 205 rear.
In the UK try Midland Wheels...Their selection is better as more type/compounds are available by manufacturer. ld