I think they can only be purchased direct from bxpanded.com . I ordered mine and it arrived pretty quickly.
I just installed mine weekend before last. Excellent instructions. Love the centerpunch stickers they provide. I made the centerpunch, used an Irwin titanium 3/16" pilot hole, then a 3/8" Irwin titatnium bit. Both at moderate speed with lots of cutting oil. Worked VERY well. Then I switched to a 3/4" bit I purchased via Amazon. I barely was able to get the two holes finished with that bit. Its pretty dulled up, but job done. I used a round file to soften the edges of the holes a bit and then spray painted (JD Green!) the insides of each hole to avoid corrosion.
I had to get bolts that are 1/2" longer than those that shipped. The side tabs fall slightly inward of the sides of the bucket. Instead of forcing the tabs outward I decided to buy two extra washers and place them between the side of the bucket and the tab - on each side. Its seems to work well.
I kind of wish the "hooks" across the blade edge were a bit longer and more ... uhm ... arched. It seems built for a sharper edge, and my JD 300CX HD bucket edge isn't very sharp. But its still on there solid and should do well. If weather holds it will be cutting into a mound of dense clay soil this weekend.