Funnily enough, the trade support for modelling on Mars is extremely poor. We therefore needed to kit bash, scratch build or 3D print pretty much everything on the layout.
3D printing is a great way of producing very limited run items. Even without a printer, you can order a wide variety of parts from Shapeways and a few others, while Thingiverse and Myminifactory provide loads of free designs to print at home.
The printers start from about £250 or so and go up well in to the thousands. All the items on our layouts were printed on Matt's heavily modified CTC 3D printer in ABS. This meant they could be filed and drilled - something that's not so easy with the more common PLA. We then painted them with acrylic paints, adding plenty of weathering as we went.
We've been asked for some of the print files, but as we did not create many of these, they will be linked back to the original files. We did modify quite a few of them either to make them easier to print or to delete and modify areas we did not need. Files were modified using Microsoft 3D Builder and sliced ready for printing by Simplfiy3D
https://www.thingiverse.com/thing:3259046 Our alien needed the legs printed separately but was worth the effort.
https://www.thingiverse.com/thing:157965 This lovely loco body was printed, finished and painted in about 3 hours.
https://www.thingiverse.com/thing:552826 We printed about 20 of these of and painted them to look more like early diving suits. Hopefully that fitted the theme.