You could use any urine that is clean. Synthetic urine is pretty cool because it comes with everything you need, but if you can't buy that, I suggest you get a temp strip to put on the bottle you put the urine in. When you give the sample, it has to be between 90 and 100 degrees, or you'll fail.
You can get the temp strips at a pet store, they sell them for reptile cages, you know? Make sure it goes at least to 100 degrees F.