Hardware or Home Improvement stores, usually in or near the paint department. It's a little pricey that way - about $7 a gallon IIRC. I can get it much cheaper from a local oil company, but I don't really need 5 gallons (or more).

It's pretty easy to store - a clean plastic bottle will do fine. AFAIK it should be OK in an aluminum fuel bottle, but why bother? Go a little fancier if you like and get a small red plastic Nalgene fuel bottle.