I found it very difficult to find references to it online. There is a reference in the "Hackers" book by Steven Levy to Sierra On-Line having one (he uses the name "Form Master"), and former Sierra employees have mentioned it as well but with the two words run together as FormMaster. As I couldn't find much more, I'm not sure which form of spelling is correct.

https://www.google.co.uk/books/edition/Hackers/JwKHDwAAQBAJ?...

There is a photograph in a September 1983 issue of a Japanese magazine called "LOGiN" of one of Sierra On-Line's disk copying machines but the article doesn't mention it by name. I wonder if it is the FormMaster/Form Master machine.

https://archive.org/details/login-september-1983/LOGiN%20-%2...

As an aside, that September 1983 magazine is the earliest clear reference to the development of King's Quest that I could find. It isn't mentioned by name but it is obvious that it is King's Quest that is being referred to.