practically speaking it isn't available in CA. unless you happennto live in the neighborhood of the aforementioned locatuins it's just not realistic.
small quantities are available at any hardware/home improvement store. i find that the 1 quart containers bought in the "contractor discount" quantity (6 at home depot) are the best deal being cheaper per vol than the gallon container. even so, you're in the $16/gal neighborhood and that isn't sustainable personally
for my experience on carb'd bike, running the carbs dry before before parking it will prevent the problems. sustained contact (i.e. parked overnight) with the ethanol swells and degrades the rubber parts, so shuttting off the petcock and letting as much gas get pulled out of the bowls as possible is a good preventive measure. if you have a vacuum petcock i don't know what to tell you unfortunately