The Iwata website doesn't show any rebuild kits. There aren't any shown in the manual, either. Before I'd buy anything, I'd disassemble the airbrush and check the wear parts, especially the needle. New seals won't seal against a worn needle. I have, in the past, been able to polish the needle if it isn't too badly worn and get the airbrush to hold air again. A little bit of paint leakage isn't really a problem. Here's the pertinent info from the manual. You may need to know the date the airbrush was made to order some of the parts.
You can go to Iwata online, and there is a picture listing of every part they sell for their airbrushes, with the part number and price.