Go to a drug store or pharmacy. Look in the household cleaning supplies section. Make sure it's labeled "pure" ammonia. You don't want to use detergent or scented ammonia.
This is kind of gross. Before there existed products, like Cycle, for starting a culture in a new setup, hobbyists would add urine to the tanks for a fishless cycle to run. Most FW keepers just added "trash fish" to cycle tanks. But, the fresh urine additive was routine for fishless cycling of SW setups after seeding with sludge from another SW setup..