With the latest Patch you can trade with almost any NPC ... and sometimes they have Spellbooks, too. <img src="/ubbthreads/images/graemlins/winkwink.gif" alt="" />
Sometimes a poor farmer, he has maybe 3 gold pieces, an apple, and a 5k spellbook for some spell! <img src="/ubbthreads/images/graemlins/eek.gif" alt="" />
IIRc, throughout the game, without random spellbooks, you can get up to level 4 restoration for free, so get level 1 first, then start doing all the other's, and you get level 5 early on!