The transformer described is a 1,000 ohm center tapped - using one half or 500 ohms. The other side is 200,000 ohms so the ratio is 1 to 400.
From what I know of transformers the turns ratio is what really matters however the impedance also matters in some situations. I don't know if this is one of those situations. Now for the confusing part - I don't think the 1k side actually measures 1k and the 200k side 200k but there are some rules of thumb on what the actual impedance should be. I recall something like 4x the actual impedance but someone else will have to confirm that. It's the turns ratio that will match a 1k circuit to a 200k circuit.
While I do believe that the circuit works I'd have trouble expecting an audio transformer to have a construction that would tolerate high voltages for any amount of time.
So in your search, look for small audio transformers with a ratio of 1 to 400 or 400 to 1 and you might get closer to what you need. Newark Electronics, MCM and others like Jameco might have them. I actually have one very similar - 600 ohms on one side and very high on the other side - made for some kind of telephone or transmittter interface.
Hope this helps.