http://www.agtannenbaum.com/
http://www.w7fg.com/
There are undoubtedly some others. Good luck!
I also have one of these testers. I would like to know more about it. For example---it has a "tube life" test, but I don't know how to use it. If you found a manual with such instructions, I will be most happy to buy a copy from you.
Call Sencore at (800) SENCORE
www.sencore.com for ordering an owner's or service manual
Good Luck!