It wasn't the first source I have tried. At first I have dropped a piece of raw shrimp with some flake fish food into my fish tank. It was definitely a bad idea. Not only it produced ammonia too slow, but it was also super STINKY! I waited for two weeks with no sign of readable ammonia. Many of my decorations were contaminated with the stinky smell. I had to remove the raw shrimp, washed every decoration in there, did several large water change before I started it all over again with Ace ammonia.
I will never use anything but pure ammonia for fishless cycling ever again. Ace ammonia comes in huge bottles. One bottle is enough to fishless cycle hundreds tanks. You will never need that much. If you have Ace Hardware nearby, it is the easiest source of pure ammonia to get. Funny they asked me what I will be using the ammonia for when I was there. "To cycle a fish tank" was my answer. I doubt it made any sense to them anyway.