I pick it up from my LBHS and add between 1 tsp and 1 tbsp to 5 or 6 gallons.
You could try a baking supply store.
My process for cloning a beer
1. Put on lab coat.
2. Drink beer and take notes.
3. Repeat Step 2 until I have a recipe or pass out.
On deck: Barleywine, Dampfbier, Belgain Golden Ale, Hazelnut Sweet Stout, IRA, Rye-weizen, Wit, Uinta Hazel Clone, Uinta Yard Sale Clone.