I had seen magnesium citrate (without the calcium, lots of stores carry only the calcium/mag. combos)in a number of health food stores, but mostly in tablet or caplet form, which would do the job. But I wanted powder or capsules, so I went to a larger store, and they carried it. I had gotten burning sensation from the ES, the magnesium citrate does not burn me at all. If you can't get it in a health food store, maybe try a compounding pharmacy, those pharmacists who prepare things on the spot. Or the internet?
Yes, I take it just like the ES, same amount of liquid, at the same times. Although I do skip the fourth drink in the morning and drink prune juice instead, just my preference.
Magnesium citrate, like Epsom Salts which is magnesium sulfate, is a muscle relaxant; also produces a form of diarhea, like ES, but a bit less so. Don't know if it has to do with the quantity I am taking. Magnesium oxide, on the other hand, is supposed to not produce diarrhea, so not good for flushes.
I had absolutely no problems passing stones, no discomfort at all, including the 3/4 inch one, they all slipped out effortlessly.