Do you mean an actual bucket that is built to fit a "Gradall"?
The Kobelco 35 that I frequently run has a 36" cleanup bucket (by which I mean it has a smooth cutting edge, with no teeth), that we often use. I'm not sure how a Gradall bucket would hook up to a mini excavator, but this bucket has the right size holes for the pins. A Gradall is a pretty big machine. I gotta think an actual Gradall bucket would be a little big for most minis to handle comfortably, but this bucket is just about right for the machine.
One of the sites we work on has very tight quarters--sometimes as little as 5' between houses, so the mini gets a lot of hours grading. We also use it inside the foundations to make grade for basement and garage floor slabs. There are also lots of times when we pick dirt or stone right out of the bed of the dump truck. The toothless bucket is better for that too. There's far less chance of doing major damage to the bed, and you can get almost all of the material with the machine.
Do you have a Gradall bucket that'll fit your machine?