Remember, it is a gasoline-like fuel, so it may be hard to ship through the mail. That may be why it doesn't appear at Internet shopping sites like Catalog City, where I can't find it any more either.
One version is called Pennzoil Roadside Rescue. You can read a bit about it at
http://www.canadiandriver.com/articl...ide_rescue.htm. It is real pricey - $25 for a half gallon - and it works only in a hot engine, but it will keep in your trunk for 5 years, ready for the time you need it. Pennzoil products are widely available, so I would expect that you could find it at WalMart and most auto supply places.
There is another version called Spare Tank, a little cheaper at $25 for a gallon container. See
http://www.rv-news.com/july1999/feature3.htm. I don't know where you would get this.
There are probably others.
Bill