I would like to build a circuit with a toggle switch linked to a small rotor, such that when the switch is moved to position B, it send a small pulse, rotating the rotor a little bit, and then when the switch is moved back to position A, it would rotate the rotor back to its initial state. Like a door/gate, that opens and closes depending on which position the switch is moved to.
I've already looked into the 555 Monostable, which is probably what I want here, but can't figure out how to make the rotor rotate in the direction I want it to.

Please do you have any suggestions? I'm also thinking anything up to 9V, if it makes any difference...

 

Two 555 timers. Both outputs normally high. Place the motor on pin3 of each chip. Use the switch to trigger one or the other monostable. Whichever one goes low determines the direction of the motor.

 

but can't figure out how to make the rotor rotate in the direction I want it to.

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For a DC motor you reverse the motor leads, either by S.S. means or relays.
Max.

 

Can you use a modeller's servo as the 'rotor'?