In arx itself, starting in the main merchant area (general merchant, potion seller, archery seller) you can head north and cross a bridge with a bunch of paladin guards. Take an immediate right and there should be a couple stands, I believe those two sell the books you need. I'm not 100% sure, though, because by the time I found them one of them was randomly dead. I don't know why people in arx seem to randomly drop like flies.
If you can find a regular blank water book, that would work with the restoration scroll you have.
