The easiest thing to do is assign a pure black texture to a rectangle object and have it as a choice somewhere.
But I also believe there are a few out in stock now. Let me see if I can find them for you.
Here is one from Rolfy he gave to the community for free.
These can be seen when placing them and not in test game and standalone.
https://forum.game-guru.com/thread/208361Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz, 2400 Mhz, 4 Core(s), 4 Logical Processor(s), 8gb RAM, Nvidia gtx660, Windows 7 Pro 64bit, Screen resolution 1680 x 1050.