Here in Southern California, Mutton is often cut into chunks, similar to how Goat is often cut, but into larger chunks. Most of the Mutton available here is imported frozen from Australia or New Zealand. The photo specimens were about 50% bone, but quite low in fat.
More on Lamb / Mutton Cuts.
Buying: Mutton is not common here in Southern California, but can be found in some of the ethnic markets, particularly those serving a Philippine community. The photo specimens were found in a large multi-ethnic market in Los Angeles for 2016 US $2.99 / pound.
Cooking: These chunks can be roasted whole and used to make soup stock. I usually cut away the meat for other uses (a little tedious) and roast the bones for about 30 minutes in a preheated 475°F/245°C oven. I then simmer the bones for stock. Note: all the fat goes in the stock pot because some of the desirable flavors from the fat are water soluble. When the stock is done, the fat is removed using your gravy separator.
Yield: These chunks usually average out around 50% removable meat and 50% bones, membranes and fat.