I had to go to the local beer/wine store that sells supplies for making beer b/c I couldn't find it anywhere else. It won't help with your lactation cookies but I also bought some brewer's yeast pills from the GNC section at my local Rite-Aid.
DS1: 8/3/10, DD1: 8/17/13, DD2: 8/13/15
Twins lost to due to partial molar pregnancy: September 2011
Nutritional yeast is the same thing - I picked mine up at a whole foods-type store called Sprouts. My local grocery store (NOT WalMart or Target) carries it as well - it's actually with vitamins and other nutritional aids.
Re: Brewers yeast for cookies