Paumco, makes them for all buckets, there is a seller on eBay that has a 74"x8" for $235 with free shipping. There add said they have other sizes available.
Dave
/ Suggestions for aftermarket 553 HD bucket cutting edge?
Because of the side reinforcements I'd say you have the HD bucket.
Discountsteel.com sell single bevel ASTM 1055 stell cutting edges in many widths, thickness, and will custom cut to length. You will have to drill to match you bucket.
For example 1/" x 6" x 6' is $101, and weighs 57lbs, so you have figure shipping.