I looked at this I thought of having a go at the circuit myself only one snag the speakers...
Maplin had some 64 ohm ones cat. no. YT27E but they don't appear to be in the new catalogue and are listed Out of stock so there probably wont be any more.
Rapide have some 80 ohm PCB mount speaker sound generators which might fit the bill perhaps...don't know how good they will be they are only 62p each.
As for the transformers...well not much luck there either vast majority of audio transformers are 1:1. So I have sort of given up.
Considering the low cost....next time I make an order for rapide I might add on a couple of those sound generators and see what happens since the circuit is so cheap to build....not much to lose if it's carp.