Where do I buy food additives (not in bulk)?
Hey guys, since the question was posted they opened up Modernist Pantry, which specifically caters to this need. They supply chemicals for molecular gastronomy in consumer-sized portions.  

For $10 or less apiece, you can order small amounts of emulsifiers, gelling agents, foaming agents, etc. They also have spherification kits, the Texturas products, and Molecule-R's lineup.