Urea has multiple uses because it dissolves well in water and is non-toxic. Urea is used as a fertilizer due to its high nitrogen content. It's used in cattle feed, for dermatology, and by those who dye clothes (to keep the color from bleeding). Urea is inexpensive and, depending on how you want to purchase it, not difficult to find.
Urea is an excellent fertilizer, but is generally needed in bulk. Some feed or farm stores will carry urea. But as with hay in recent years, it is easier to go online, where you'll find many different options and prices.
Urea is also used as a feed. Cattle, goats and sheep are given urea in their feed or in salt licks. Urea in this form can also be found at feed stores and suppliers online. Elitefarmer.com is a good source of this information.
Those who dye clothes use urea to keep the dyes from running. You can use the same urea you get from a feed store if it is clean and white, but dye stores also carry urea, including Grateful Dye and Blick.
Urea is also used in dermatology, because it is so water soluble and makes the skin soft with the help of other agents such as lanolin. Topical urea is easily accessible from your dermatologist and drug stores.
Humans produce urea through urination and sweating.