Which country/region do you live in? Different areas have different shops. When in doubt, go to Wal-Mart. It might be depressing and annoying, but they have just about everything. A home improvement or hardware store may also have it.
Some grocery stores and convenience stores have it as well. Or you could just mix distilled vinegar and water 50/50 in a squirt bottle. Doesn't smell as nice, but it works.