You should be able to get it from Farm Service (FS) or whoever delivers fuel to farmers or other businesses. I can get it easy off the shelf at the CO-OP, so it shouldn't be hard to find.
If you don't have problems with algae growing in your tank, I wouldn't worry about it. I don't know what state you are in, so I'm not sure if it is even a problem down South or not if you are there.