Not sure about glucose, but Rainbow had glycerin for food use when I was there a couple of weeks ago. If you don't want to cross the bridge, you could also try Sugar'n'Spice in Daly City for glucose. It's a bit musty, but has a lot of decorating sugars, molds, etc.
1745 Folsom St, San Francisco, CA 94103
2965 Junipero Serra Blvd, Daly City, CA