I have used LEF Magnesium Thronate powder for years and it works well. I mix it with other powders and take it twice daily.
You can get it from iHerb or directly from LEF. [
www.iherb.com] I buy most of my supplements from LEF during their annual sale but I occasionally get burned when I decide to change a supplement during the year.
I buy as many of my supplements if powder form for several reasons: no mixer or dyes in them, cost, easy to modify doses, etc. Other good sources are Pure Bulk Bulk Supplements.
Godon