The Sylvania guide I checked for my 2003 shows the rear turn signal lamp #7440A (Amber Bulb). You don't have to go to the dealer, go to your local auto parts store. They should have an application guide for the brand of bulbs they sell. Also take your burned out bulb to the store as a sample so they can match it up.
That's exactly what I did....I had the bulb in my hand at Auto Zone and compared it to every bulb in the aisle. Nothing matched, so I looked at the Sylvania application guide and it said they don't have a bulb to match our rear turn signal bulbs. But I think you're right about the 7440A part number....I just can't find it anywhere.
The funny thing is that our owner's manual has a chart in it with all the replacement bulb numbers, but the rear turn signals are left blank. Weird.