You've got the key points, it gets pretty complex when you start looking at all the possible interactions. Glutamate can come from MSG, aspartame, inflammatory states, and protein rich food too. It's not unusual, there's lots of vitamins/minerals which compete with each other for absorbtion.
Dairy, meat, garlic, onions are some good sources of sulfur.
One of the first marketed glutathione boosters was a high quality whey protein called Immunocal. The human clincals on that (http://www.nutrition...es_body.htm#a19
) showed an increase in lymphocyte (white blood cell) GSH of ~35% while the NAC based MaxGXL formula showed in the human clinical trial an increase in lymphocyte GSH of ~276% (http://www.getmaxed....GXLAbstract.pdf
). So there is a big difference between supplementing with high cysteine/sulfur foods and with cysteine pro-drugs.
Looking at the wikipedia page Glisodin contains the anti-oxidant enzyme Super Oxide Dismutase (SOD) which is produced by the body. An alternative way to boost it would be to take foods/supplements which are Nrf2 activators. These increase the production of a wide range of antioxidant and detoxification enzymes, the enzymes which synthesize glutathione and more. The best known/most studied ones are sulforaphane, which is highest in brocolli sprouts, and curcumin, the yellow pigment in tumeric.
These plant extracts which are Nrf2 activators have been shown to boost glutathione levels by increasing the enzymes which create glutathione. You'll notice the Cellgevity product (http://www.getmaxed.net/max-cellgevity
) has these in them, combined with the RiboCeine, so you have both the increased cysteine and enzymes for glutatione.