Instead of trying to buy a 40 years old audio transformer to use in a high voltage circuit, use something modern that makes a high voltage.
A disposable camera has a high voltage circuit that has a nice little transformer and the entire circuit to make about 350VDC and a pulse of about 4,000V. Stores that print pictures for those cameras throw away the part with the circuit. Get one or two from them for free and use the circuit or its parts.