"It's his eyes, Roland thought. They were wide and terrible, the eyes of a dragon in human form" - Roland seeing the Crimson King for the first time.
"When the King comes and the Tower falls, sai, all such pretty things as yours will be broken. Then there will be darkness and nothing but the howl of Discordia and the cries of the can toi" - From Song of Susannah
I think that the 'grandfather fleas' show up in yet another King book, 'Needful Things'.
It's mentioned that the necklace Polly gets from Gaunt makes insect like sounds and such...it could well contain a grandfather flea. And our man Gaunt does get around. He could easily have picked one up somewhere.