When the exteriors were filmed for that episode, at TRW in Redondo Beach, California, a couple of Trek fans who worked for the company had this photo taken in their homemade uniforms and makeup. Over the years, Star Trek has inspired countless fans to get deeply into it, but this photo shows that these two girls were big fans even in 1967. Sorry for the quality of the photo, but it's rapidly closing in on being 50 years old and it's the only one I have. Received it about 10 years ago as a bonus when I bought some other Trek material.
On one of my trips to LA I visited this site and took some pictures. It is now a Grumman Northrop complex. The exterior building we see still looks the same. http://www.imagebam.com/image/900edf230539949