Best bets for all of our nutrients come from foods. Our body knows exactly what to do with them.
So for Magnesium: dark chocolate ( smile), tofu, edamame, avocados, whole grains, cultured yogurt, black beans, leafy greens (kale, spinach, mustard, collards, turnip greens ), pumpkin seeds, chia seeds.
I buy the edamame in freezer section and then fill a pan with a little water and bring to a boil then turn down and let simmer for about 7 minutes. Then cool, sprinkle with a little good quality vinegar and a pinch of salt. They pop easily from the pods and are a delicious snack while I watch sometimes depressing news. It cheers me up just a little.