Dr. Christopher's Calc T is actually not very high in calcium. It is high in silica, which is very helpful in helping the body to effectively utilize and regulate calcium. In the case of arthritis, I would definitely suggest using Dr. C's Calc T as AJ describes. If I were to pick one of the herbs to add to Superfood for the silica effect, it would be the horsetail. Otherwise, you can make the Calc T yourself and take it in capsule form separately from superfood.
Alfalfa is very high in calcium and it is part of superfood. You could add some of the brassicas like broccoli or kale as they are high in calcium.
Personally, I would start with the Calc T. In general, Americans have a lot of calcium in their diet, but the body utilizes it poorly. The Calc T will help with that.