Here's a simple circuit I made as an HV source. I wouldn't advise using it though. Using a taser for self defense is retarded. Use a 1' piece of rebar or something.
If you insist on building it, though…
>Use 1N4007 for the diodes
>Use a BC347 for the NPN BJT
>Use a voltage source between 16 V and 3 V
Use this to learn about electronics, though. It's a very useful thing to know. I'll post a bit more technical data.