Answer: A gram is a unit of measurement for mass. A liter is a measure forvolume. Because different substances have different masses, theamount it would take to make a milliliter will also vary.Therefore, there is no set number of nanograms that converts tomilliliters-- it depends on the substance being weighed andmeasured.
Answer: You can purchase artificial vanilla extract from pretty much any grocery store - look in the baking goods aisle by the spices. If you are looking for natural vanilla extract, you can generally find it side-by-side with the artificial stuff, but the price will be several times higher.