@Yoda
I recently bought some doors from Corvus Games Terrain (see page 1).
The first set were too large for my existing buildings so I asked them to print me six doors at 80% (I also gave them dimensions).
This was no problem to do and also cheaper than the first set.
I had them within a week.
I am not sure how this works on Shapeways but If you can contact Mel, I am sure that he will be able to shrink the files.