Several years ago, I borrowed a telephone test set from our local phone company office.  It was perfect - it would ring any of the standard frequencies (in the "old" days when phones were on party lines so each phone was set to ring on a different frequency so that only the right phone rang).  Several of my older style phones require one of these seldom used ring frequencies.

The test set was in the booth and I used mike cables to run from there to the stage where it connected to the wires from the phone.  There was no magic to using mike cables except that we had lots of them.   Unfortunately, after five or six years, the phone company remembered that I still had the test set and I had to give it back.  I still borrow it when I need it. 

I am building a ring generator myself, if I ever get around to it.  It is not complicated and there are lots of circuits available on the internet - maybe you can get an electronic hobbiest to build one for you - the parts cost about $15.

Doug