I believe Kippo Models can supply their excellent model building ready painted at a cost. Not sure about platforms, too many variables in terms of height width, length. I have ten Kippo Models buildings, but then I assembled, kit bashed and painted them all myself. Their new 3D printed models are easier to assemble that their old resin cast models. There are tutorial videos on YouTube that show you how to paint them, worth having a look and perhaps trying it yourself.
Link to Kippo website.
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My old style resin cast kit for the Claptowte Railway with link to how I built and altered it.
Claptowte Railway - Gernise End Station Building
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David