For that it's tough to recommend. I estimated my store-bought taser had a turns ratio of 1:285 to 1:200 which was stepping up discharges from a 350-volt spark gap oscillator. [Assuming the shock voltage was the 100KV it was advertised as]. The transformer would have to built for the high-voltage taser application or else the secondary coil will experience dielectric breakdown (among other problems). The only retail vendor I know of that caters to this spec is amazing1.com but theirs is "only" a 45kV transformer.
The frequency on your oscillator also has to be controlled to operate in the LF region (50kHz is typical) or else it becomes highly dangerous. Additionally, the oscillator has to be current-limited to avoid moving a hazardous charge--even for small load resistances, which I'm in the process of researching. There's a lot of controversy involving tasers (most of it scaremongering), so my best advice is to just take a professionally-built taser and create a supply cut-off switch.