lol i didnt even have to use google to find where to buy some ore online (not in stock often though).
http://www.unitednuclear.com/uranium.htm
they also have the first half of the process (The extraction part) on their site for how to get the uranium out of the ore. the chemicals required are sold in their chemical supply store elsehwere on their site
http://www.unitednuclear.com/extract.htm
now of course, the ore you will be using from their site isnt as high grade as the **** they just took out of iraq, but it can still be used in the creation of dirty bombs if you get enough of the stuff and refine it