Okay so it looks like I've found a way to get some Nichia 5mm LEDs into the states for a reasonable price (Thanks Fichtenelch). Now I need to figure out what I'm going to use to regulate the current for 3 or 4 in series. I was hoping to find a driver with two or three modes (50mA, 20mA and 10mA), but I am having trouble locating anything that will regulate such a low current. I will be using a single lithium cell, so the input voltage needs to be around 3.6v.
Although a multi-mode driver would be ideal, I have thought about using a resistor, if I can't find an acceptable driver. The problem with this is that I have never used a resistor in a light before and have no idea how to determine what size I would need for the desired output.
I would greatly appreciate any sources for drivers and/or any information on how to determine the size resistor I would need in order to run 3 or 4 LEDs at 20mA safely and efficiently.