What type of transformer is this?
As a first pass, I'd say you are probably looking for an "audio transformer".

Update: I'm a bit concerned whether you're fully aware of the type of signal you need. Is this intended to test phone wiring? If so you might want to read this:

http://www.epanorama.net/circuits/teleinterface.html

I don't think you need 40V signals for them to be audible in a phone handset. Indeed, I recall connecting them via 1:1 transformer to record them on a tape recorder, which suggests signals in the 1V range.