I have seen that blade arrangement on a Yard Man (MTD) lawn tractor of the same era as the 1225. Since the 1225 was made by MTD it would not be unusual to find them on it. It is a mulching blade and the MTD part number is 942-0539.
http://www.partstree.com/parts/cub-c...arts/942-0539/
There are tons of them on eBay..../
https://www.ebay.com/sch/i.html?_fro...2-0539&_sop=15