Unless he's run out, there are full spellbooks for sale at the Yew moongate.
There is also a vendor at the Brit moongate that sells scrolls. Typically they're Recall, but sometimes there will be Mark and Gate scrolls as well.
Yeah I checked Yew and couldnt find any spellbooks. If anyone would take an order ill pay 1000 gold for a mark scroll.
I've put up a few mark scrolls on my Brit Moongate vendor (leftmost vendor), no need to pay such a high fee; it's only 80 gold.
will have full spellbooks back on later today