There are no microphones that directly produce a "Robotic sound effect". But there are available instrument, gadgets, and synthesizer program that produce a "Robotic sound effect" using a microphone. And you can find and buy them in ebay.
They are:
1. A "Vocoder" (pronounced /ˈvoʊkoʊdər/, short for voice encoder) is an analysis/synthesis system, mostly used for speech. In the encoder, the input is passed through a multiband filter, each band is passed through an envelope follower, and the control signals from the envelope followers are communicated to the decoder. The decoder applies these (amplitude) control signals to corresponding filters in the (re)synthesizer.
http://en.wikipedia.org/wiki/Vocoder
2. A" Talk box" is an effects device that allows a musician to modify the sound of a musical instrument. The musician controls the modification by lip syncing, or by changing the shape of their mouth. The effect can be used to shape the frequency content of the sound and to apply speech sounds (in the same way as singing) onto a musical instrument, typically a guitar (its non-guitar use is often confused with the vocoder) and keyboards.
http://en.wikipedia.org/wiki/Talk_box
3. "Auto-Tune" is a proprietary audio processor created by Antares Audio Technologies. Auto-Tune uses a phase vocoder to correct pitch in vocal and instrumental performances. It is used to disguise off-key inaccuracies and mistakes, and has allowed singers to perform perfectly tuned vocal tracks without the need of singing in tune. While its main purpose is to slightly bend sung pitches to the nearest true semitone (to the exact pitch of the nearest tone in traditional equal temperament), Auto-Tune can be used as an effect to distort the human voice when pitch is raised/lowered significantly.
http://en.wikipedia.org/wiki/Auto-Tune
Artificial Larynx device is like an ordinary portable microphone with built in audio amplifier that is used by the person who have lost their original "voicebox" (larynx), usually due to cancer of the larynx. This mic cannot reproduced a Robotic sound effect if used by a normal person with a healthy larynx or "voice box"