You could try the parts bins at your local Radio Shack.
They had those small bulbs last time I needed one.
It was a bulb with the wires already attached. I cut the old pigtail off at the bulb, stripped the wires on the new bulb, and where I cut the old bulb off, and soldered them together, using heat shrink tubing to secure the connections.
Still working to this day.
I used a 12 volt bulb, which is what I needed in my application. You should check the voltage on yours before you buy a new bulb.