Powdered Vitamins and Minerals at ALL ONE is the official web site. Can't speak for every health food store, but the one local to me sells All One.
I followed Meditation Mama into the world of L-Trpytophan. Her post #16 in this thread gives a good explanation of how it works daytime and night time. I've been taking 500mg in the AM, and 500mg at bed time.
DG