I'm sure urea is easily avaliable, unless it was banned when I wasn't looking. Some things have been lately.
Its used to put on the stumps of felled trees, to stop some sort of infection into the root. At least thats what I understood it to do. I did quite a lot of it when i was a kid.
Dont really know where you get it from, but shouldn't be a problem. If its the right variation of the stuff or not, I dont know.