Misty Mountains:
I found many while doing Epic book 5. This book sends you to Goblins, and there are instances with Dourhands and Angmarim, all of whom drop pages. Besides the goblins, I also spend some time farming the bitter stair (pages and rep items) and the Dourhand enclave.
Angmar:
Beginner quests from Earth Kin send you to Ram Duarth to deal with Orcs and Angmarim. While doing quests out of Aughaire, you have to take on various Orcs, Hillmen, and Angmarim. I usually finish when I reach the Orcs in the eastern part of the zone.
My latest attempt, starting at level 39, I (finally) got one book done at level 42, and finished the first three by level 45. To get the 4th legendary is still a pain! Looks like it is skirmish time to finish that one.