The International appears to be a private brand applied to a mainstream mower, so the blades will be generic. You could just take one of the blades (complete with it s mounting hardware) to a mower shop or discount auto shop and see what they have. Make sure you install a matched set, since they must all weigh exactly the same, including the pivot bolt etc. Your mower can be fitted with either 2 or 4 blades.
Most likely someone will be able to tell you what other name or names the mower was sold under, by recognising the base. The blades look extremely similar to the ones for my old 1976 Victa.
You can find out the age of your mower by giving us the engine code number: a very long series of numbers, in groups, stamped onto the red air cowl at the top of the Briggs & Stratton engine. The last block of numbers gives the date it was made. Looks to me like the first block of numbers might read 92908, and it might have been made before 1980, unless it turns out to be bigger than 9 cubic inches displacement. (The 9 cubic inch engines were de-rated to 3.0 hp in about 1980, when their maximum speed was cut from 3,600 rpm to 3,000.)
