My son Alan produces 3D models, mainly of narrow gauge prototypes; however over the last few months he has been working on a 4mm scale 3D bubble body , to be used in conjunction with the Dapol Prestwin kit and the SSM detail etchings.
The bubble is now available via his Shapeways site:
http://brackmodels.weebly.com/cie-cement-bubble-in-4mmft-00.html
I have the 3 test models and he says a further batch of 4 are now just about ready for me.
ERnie