Donald, I would have thought you should be able to get them there, urea is a nitrogen fertilizer. You'd have to ask at a farm supply store maybe, or perhaps a nursery/garden centre - although Google suggests Home Depot in the States has one nitrogen fertilizer that is ammonium sulfate combined with urea.
This U of Minnesota page says urea can be purchased as prills or granules, so must be available at least in that form in the States:
http://www.extension.umn.edu/a...
