I need a powersource based on locomotion (3V 20 mA)
That won't work, you can't generate the needed power to light a lamp that way. It works for the watch because that uses about 100 000 times less power than the bicycle light.  

What's wrong with your dynamo? If the problem is that you have to peddle harder, then the sideways motion to electrical power conversion doesn't help. There's the Law, more specifically the laws of thermodynamics. They say that you can't get power from nothing. For the dynamo the penalty for getting electrical power is to exert more mechanical power. Same for the sideways motion. If you would be able to create enough power for the lamp you would feel a mechanical resistance reducing the motion, so instead of having to peddle harder you'll have to exert this force sideways. 

There's no such thing as a free lunch.