In what quantity? How much citric acid would you have to take to get 100 mg of Oxaloacetate? Plus, all supplements sold without a prescription in the U.S. have to naturally exist within the body or be in "normal" foods. If resveratrol had proved to have anti-aging properties buying it wouldn't be a ripoff even though resveratrol is in red wine.
http://en.wikipedia.org/wiki/Citric_acid#Occurrence
47 grams per liter of lemon/lime juice. That converts to ~25 g oxaloacetate per liter. Oranges apparently have less citric acid, to the tune of perhaps 500mg oxaloacetate equivalent per liter of juice.
For those who are interested in this topic, I'm just wondering what longevity research today looks most promising to you and why. Whether that's SENS, cryonics, nanotech, brain uploading, etc is fine with me. Any links to actual research papers would also be greatly appreciated. I'm very interested in longevity, and am curious to see if anyone else would like to offer some thoughts on the current state of the art.