Printable Scenery is a company that sells STL files for various bits of wargames scenery, from walls to houses and a few things in between. STL files are the model files which describe the subject in 3D and can be used to actual print the subject on a 3D printer. I bought the walls and fences products - both come as a selection of STL files which you can use to print your own walls as many times as you want.
Without further ado, the photos below are of my first test prints as they came out of the printer (I used black PLA) and painted:
While the grain on the raw printed wall is quite visible (I used 0.2mm layer thickness), once painted with a quick layer of black gesso and then dry brushed with various greys, they look fine.
I think I'm going to print a lot more :).