The BBC is sharing some of the sound effects they used on the radio in the 1960 as part of a broader Web audio project they've been working on. In the collection called Recreating the sounds of the BBC Radiophonic Workshop using the Web Audio API, they offer explanations of the effects and the technical information associated with the API (which you don't need to understand), and most importantly they offer that you "have a play" with the virtual devices. The Wobbulator is calling to you.
It is apparently possible to use your computer's microphone to make your own Dalek sounds with the Ring Modulator, but I haven't had a chance to play with that yet. Let me know if you get it to work.