Jarrow is a good quality brand, as are the others mentioned.
Food sources of L-carnitine include red meat, dairy, tempeh, wheat, nuts and seeds, legumes, certain fruits and vegetables such as asparagus and avocado, and peanut butter. Many whole grains contain carnitine, such as buckwheat, corn, millet, oatmeal, rice bran, and wheat germ. Lamb is especially high in L-carnitine.