Your best bet would be to go back to your LFS (local fish store) or where ever you purchased your turtle and get a bulb there. Remember, in the future to do plenty of research prior to buying the pet. It should always be the last thing you need as far as necessities go. Stress is normal for a new pet and continuing to change his surroundings will only add to that stress level. I'm assuming you got a red ear slider (correct me if I'm wrong), so here's a link to some info you might find helpful. http://www.redearslider.com/
Pretty simple name right? If you've already done your search and just forgot the bulb, then I apologize. Only trying to help.
Could we get a picture of the tank set up and the little guy?