Lamb kidneys are eaten by pretty much every culture where lamb is a significant item in the diet. They are similar in size, shape and taste and are generally interchangeable with pig kidneys (unless you're a Muslim or observant Jew). The photo specimens were 3-3/4 inches long and weighed 3-3/4 ounces each.
More on Lamb Innnards.
Buying: These can be found in markets serving communities from countries that use a lot of lamb: Turkey, Armenia, Middle East, North Africa, Pakistan, etc. They should not have a strong odor.
Prep: Split kidneys lengthwise as shown in photo above. Cut out the white fat and any attached plumbing.