Potentiometer current rating
I doubt you will find a suitable potmeter. Standard carbon potmeters allow only a few mA, and even wirewound potmeters won't take 10 W. Because that's what we're talking about. The power dissipated in the potmeter will be at a maximum when the lamp power is set to 25%, but the current will be at a maximum when the lamp power is set to 99%. Also control is anything but linear.
A (linear or rotation) rheostat may work, but they're expensive and not easy to use.
I'd suggest to look for a low voltage dimmer, that's what they're for.