How much of an electronics geek are you, and how soon do you need it? Given a little time for me to design it and a little time for you to build it, it should take about $20 worth of parts.
A long, long time ago, at Great Lakes Naval Training center, I taught the care and feeding of dial telephone systems. The vast majority of U.S. phone systems use 48
volts DC when you're talking, 90 volts AC at 20 Hz to ring. A
circuit to generate 90 volts at 20 Hz shouldn't be difficult... I may even have most of the parts in my junk drawer.
John