For those with EG&G sensitometers that may be following this thread, I found a source for the FT-118 tube. http://www.electronicpartsupply.com/

The Radio Shack tube was nice because I was able to get it in a moment, and able to verify the sensitometer was in working condition quickly. Now that I know I will keep the sensitometer, having the original tube for less than $10 will be great.