I've been wanting to do this for some time. Here's a complete list of all the spells in Frostgrave. I've added numbering to the sheet, so you can use it for random spell finding.
Just ask google 'random number between 1 and 122' whenever you found a grimoire.
As a Witch player it's bothered me, that i can't find beast crafter grimoires unless we go dungeon crawling. And that the Forgotten Pacts spells was forgotten on the supplement treasure table.
After reading the Maze of Melcor expansion, I see no banlance issues in getting the Pentacle spells not as scrolls. Nightmare was the worst before, but with the new XP rules, it's not a problem.
Let me know if the link is broken at some point.
Lastly - buy yourself The Grimoire! It is awesome