Those look like "Disc Mower Blades"...
I have seen long ones like you are describing, I just can not remember what mower brand they were made for...
They look something like these... but longer...
Disc Mower Blades
They come in right hand OR left hand... (Right Hand, are designed to mount on a disc that rotates Clockwise as viewed from over the top of the rotating Disc, looking down)...
(Left hand the disc rotates Counter Clockwise)...
They also come Flat OR wit a bit of offset...
I will look at tractor supply next time I'm in to see if I can spot some... :smile:KennyV