Unfortunately, unless you can find another saw like the one you have with that part, you will probably not find repair parts. Too old.

I think the proper term is "collet" if that's any help.Search flea markets, yard sales and ebay to find a twin to cannibalize, or make yourself handy with machine tools and fabricate one.
Casey

Thanks sombreuil_mongrel for your input. The 4 page Sears Jig Saw owner's manual I downloaded from the internet states that it's called a chuck. Thanks Joe789

I found a BLACK & DECKER JIGSAW BLADE CLAMP & SCREW #74456-00. Does anyone know if it fits saw model # 7517. Thanks Joe789

I also have a Black & Decker 7517 which I love. Wondering if anyone can advise on a replacement for the blade? Have been checking and some say blades need holes ?? and some say they need something else................now confused. Thanks!

The part is called a Blade Clamp DeWalt part #74456-00. Same part fits the old B&D's.