Sub-Singularity I Shinjuku: Shinjuku 2-Choume free quest is the best AP & time saving location to farm Forbidden Page. You'll get about 3x Forbidden Page by spending 210AP.
4th Singularity London: Hyde Park is a location where you can farm both Forbidden Page and Evil Bone.
Here is a list of servants that need Forbidden Page to perform Ascension and Skill Up.
Rashoumon event (Ibaraki Douji event)
Murder at the Kogetsukan
Inheritance of Glory
5 Star Servants Tier List: Best Servants [5/9 updated!]
Best Servants [★4]: 4 Star Tier List
Halloween Strike! Event Missions [JP Halloween 2017]
Best Craft Essence: Craft Essence Tier List
Cu Chulainn (Alter, Berserker)
Jeanne d’Arc (Alter)
Cheer for Master
Demon King of the Sixth Heaven
Talk on the Heated Sands