Cooper Wiring devices stock # 734. We did Assassins last year and used these to ring the portal with chase lights. The bulbs you want are probably either a A19 or G16.5 20 watt or lower. Iwas going to post Cooper Wiring devices catalog for reference but it's too big. Just google them. They also sell traditional "brew cord" sockets and ceramic bases and everyting you could want.. Good luck, Great show.
For your project, you could probably use the medium screw base pin sockets without side clips, but mine was mounted in foam and they helped the sockets stay in.
You have alot of bulb choices. You could use the 7.5 Watt S11's like I did, or 11 Watt S14's, the 7.5 watt G12.5's, or the 25 Watt A19's. All common sign bulbs.
If you wanted to go to a smaller screw base, say candelabra or intermediate, you could use the intermediate base S11's (same base as a C9 Christmas bulb), or the 6 Wattcandelabra base S6, 7 watt G8 or 10 watt G12. (All same size base as a regualr C7 christmas bulb)
How big is this sign going to be, and do you want to light up the letters and the boarder, or just the boarder? I decided to light just my boarded because doing every letter in "High School Musical" got more expensive than we wanted to spend, however, Kit Kat Club should be more do-able. The pin sockets are the cheapest thing you will find, ceramic bases will definatly run you about $2.50 a piece. Take some time and explore Action Lighting, they sure gave me alot of possible ideas when I was building my sign. I personally love the classic effect of sign bulbs outlining letters. Reminds me of old movie palace marquees. Good luck with your project.