Lye, whether Sodium Hydroxide or Potassium Hydroxide, can be obtained through a scientific or chemical supply. ("Chemicals" in the yellow pages)
Usually there is a minimum amount with wholesale suppliers, so depending on how much (or little) you need , you may wish to consider looking into suppliers (online and off) for leather tanning, soapmaking and candlemaking. I did a quick search on the "About.com" search page and found a list of suggestions for online supply companies at: http://candleandsoap.about.com/od/coldprocesssoapmaking/a/lyesources.htm
I've been looking into this lately because our Native American club at my college was just gifted a large elk hide that appears to have been damaged, but is still in great shape to salvage into rawhide for drum making this spring.
Jenn, AKA Team Nashoba