I can try help you a little -
Firstly , is the dynamo a DC out put or AC ( such as a bicycle dynamo) . If the latter, you have to use diodes to first rectify to convert to DC. If DC output, then you need to use a Voltage regulator to regulate the VOLTAGE on its input to a lower voltage on its output.
Some terms :
Volts are the electromotive 'force' driving the amps ( current) into and through your circuit ( the 'lamp')
There is a law called ohms law which says - amps in the circuit = Volts applied / Resistance of the circuit.
So applying 1volt to a lamp of 1ohm resistance will cause 1 amp to flow.
Now, if you need a lower voltage for your lamps you can use a volatge regulator such as the LM78xx series. It is a 3 legged electronic device, one pin is positive input, one pin is 'ground' or negative input, and the other pin is positive output. Connect the dynamo tween positive in and ground, and the lamp tween positive out and ground.
An LM78xx is available in various voltage outputs, where the xx is the volagee - common ones are LM7812, 7810, 7809, 7808, 7806, 7805. There are similar types, a different shape to teh 78XX, but operating in the same manner, with 3.3volt outputs. (by linear technologies, the LT1086 series)
However, most of these regulators can supply a max of 1 amp, and the device needs tio be fitted to a heatsink of aluminium, of sufficient size to get rid of the heat.
There are other types of different construction, heatsink also required, that can provide more current.
All these regulator types are called 'linear regulators' and they 'convert' the input voltage to another, lower , output by dissipating that excess over itself. So for example, the 3volt output would mean that up to 9 volts be dissipated over the regulator. Since you require up to 3amps at the 3volts, that means that the regulator must dissipate 9volst at 3 amps = 27watts! A heck of a lot of heat, and would need a heatsink of around 200 Sq cm...
Another type of regulator is the switchmode regulator, a much more efficient device, more costly, and not as easily implemented. These generally have inefficiencies in the 90% plus, so need very small, if any, heatsink.
Perhaps a way for you is to use a simple BEC ( from the RC world) Regulator, that gives 5 volts out, some of them capable of up to 5 amps, and can take inputs ( usually from LiPo batteries, of up to 22volts or so. One of these can feed you RC system straight off, and then use a 3.3 volt linear regulator to convert the 5v to 3volts - this was the 3volt regulator will only disspiate 2v X 3amps = 6 watts instead of 27watts..
Also, the amps that the regulator can supply only influences the amps that you can use in the lamp - ie, a 5 amp regulator can only supply a max of 5 amps, but if the connected load or lamp only needs 3 , it will only draw 3 amps, if the applied voltage is correct ( all from ohms law above..)
Just some ideas - please ask if you have more questions.
Most of linear regulator type are available from reasonable electronic parts stores ( not sure where you are located)