Just find anything that comes one when you want it to factory. You already know what you want to tap into. Get out your multimeter (if you don't have one, you probably shouldn't do diy electrical on your car), check the voltage, if it's what you need, tap into those wires. In this case, i would tap directly from the wires in the door pannel and not the fuse box because i'd rather hack my wiring at the end than at the beginning, that's me.
Sorry, i might sound like an asshole but if you don't know what wires and can't figure it out yourself, don't do it. One of the worst ways to modify your car when you don't know exactly what you are doing is messing with the electrical system. Even if you don't damage anything, you can blow fuses and never know what is going on and what you have to fix. My friend bought a truck with a strobe hooked up wrong and it caught on fire. At the worst, you destroy the resale value of you car if you are honest to why your interior lights don't work.
