Without going into a lot of detail.... Pure ammonia has the formula NH3, and is a gas at room temperature.
"Household Ammonia," which is actually what you want, contains approximately 5% to 10% ammonia (by weight). It's the result of adding ammonia to water, which produces something called "ammonium hydroxide" and has the formula NH4OH, and is a liquid at room temperature.
So what you're really looking for is "household ammonia."
You can purchase this in grocery stores (including Walmart). Get the type that is unscented, and has no other additives. (Avoid the 'sudsy' ones, the colored ones, and the 'lemony' ones.)
You should see the ingredients listed on the label as: water, ammonia. (EDTA or tetrasodium EDTA is OK.)
The exact concentration should be listed on the label. (The cheaper ones are usually at the lower end.)
Here is a link to the one that Walmart sells: http://www.walmart.com/ip/Great-Valu...64-oz/13023511
Be sure to read the 'caution' information. For example: Use the ammonia in a well ventilated room! The fumes can irritate your eyes, nose, throat and lungs. You can wear latex or nitrile gloves to protect your hands. Etc.