I may be going mad, but I cannot seem to find the skill-learning book for Identify Item in game. Forgot to take the skill when I started the game. I have tried every library shop in every town with no luck.
Can anyone else confirm it is possible to buy from a shop?
What is the store refresh time? I've waited a month but they all had the same stock still.

Yes, I remember it popping up fairly often. To check I just loaded my last save game of a game I recently finished and found it in
Thronheim x2, Thjorgard, Guberland, Strumford.

It also dropped in random loots.

Looks like you were just unlucky. In my game I was looking for Identify Monster and no library had it for some time till one restocked on it.

By the way, the scrolls are determined the first time you check the store after a restock. So once a restock has taken place, you could save and then keep reloading till you get what you want.

I don't remember the restock times being very long. According to this:
http://www.zimlab.com/wizardry/recovered/flamestryke/mm9/miscdata9/shoplibrary.html
it's 2 weeks for every one, except the one in Frosgard.