Tiffany,
Town & Country Hobbies has a large supply of them in different voltages, both bayonet and screw in type, Train Electrics, one of our OGR sponsor does also. Both work really well, I have them in many of my older cars, like the Lionel Fish Tank Car and original GP7 Lionel engines. They also fit all the old Lionel 022, 711/072 switches and controllers.
PCRR/Dave