I did a little bit of looking into this. The only soluble supplements that are suppose to increase glutiathione are the lypo-spheric GSH and another one named Immunocal. They are both higher cost but still cheaper than the shots. I also saw they make liposomal forms of vitamin c and R ALA. I may give them a try as well.

Some good info here that talks about boosting glutiathione with foods, shots, supplements but they are trying to sell the Immunocal so some of the information could be biased.