I have been looking all over for this light and can't find anything anywhere. I don't think the bulb is replaceable.? The bulb has two wires coming from it and goes to the prongs of the plugin like they are soldered on. I know it's a long shot but if someone has one that works or a new old stock they would want to sell please let me know. I have a 75 f250 with the np203 in it that I am restoring and when I went to take it out to see if I could replace the bulb the plastic broke on me. The first pic is one I found on internet and the second is mine, showing the plastic housing broke.

 

I did a search for you and unfortunately no dealer or obsolete supplier has any.
The only one I found was the one on E-bay that they want $150.00 for! That's the one you posted the picture of.
I had a NOS unit I sold a few months ago for $25.00 including shipping . I bought it from a Ford dealer for $18.00, should've kept it.
You probably already know, but the P/N is D4TZ-10C915-B

 

Haha somebody got a deal!! Ya that's outrageous for a used one especially if you can't replace bulb....Might install it and two uses later bulb burns out. Thanks for checking!

 

One could wire in a small single led fixture of some type...cheap 12v test light comes to mind. A marker light replacement pigtail would provide the socket also and any heavy colored plastic 'lens' from any flat packaging might work...leds are warm but not hot enough to melt things, I don't believe. One might find tiny pieces of glass at craft and bead stores as well. I build scale models and just like these trucks, each 'kit' is a separate project within the whole, and as such deserve attention to detail.