looking for mag citrate without artificial sweeteners

I have to do a prep for surgery. I'm supposed to take 1 bottle of magnesium citrate, but all the products I've found at the local grocery stores and pharmacies are loaded with artificial sweeteners, flavors and coloring. Red #40! I don't want to end up in the ER the day before and postpone my op by at least a month.

Does anyone have an idea where I can find mag citrate that's clean? I've read vitamin world, but there isn't one around here.

Thanks for the replies.
I did ask the pharmacist and the doc is clueless. I'm not looking for a supplement - not Cal-Mag tablets. I need the bowel prep liquid.

I don't want to be like I am today after eating a couple of swallows of the fast food shake I ate on Tuesday. It had a bunch of undeclared artificial sweetener, color, flavor and fillers. I tasted it and threw it out, but what I swallowed was too much. I've been on the couch or the pot all day.