with a little bit of file work and a hacksaw or cutting wheel you could use just about any sawzall blade you want. It would probably be easier than trying to track down something old like that.
For sale is this Lot of 3 LENOX 4"x1-1/4" #20945-4CS 8TPI Compass Saw Blades. Made in the USA. Hardened teeth that will cut through sheetrock, wallboard, wood, plastic, and nail-embedded wood.
Discover how ASMC will meet all your needs as a reliable industrial fastener supplier and distributor, offering quality products at competitive prices.
My Dad had a Craftsman keyhole saw (probably late 1950's-early 60's). I still have it but haven't used it since I was a kid building treehouses in the county park behind our house. BTW, you have the blade mounted upside down.