Cartomancer spells?

[Sarvis the Buck]

So, trying a Witch for the first time. Was Told the Cartomancer archetype would be fun.

My only issue is that I have no idea how a Cartomancer could learn new spells outside of leveling.

A normal witch's familiar can share spells with the familiar of another witch. But I don't think a familiar can teach anything to a deck of cards.

[Grailknight]

The deck is your familiar so you add spells to it by buying cards the way wizards buy spells.

[Saethori]

Cartomancer wrote:

Spell Deck

Each cartomancer carries a special harrow deck that allows her to communicate with her patron. Its ability to hold spells functions identically to the way a witch's spells are granted by her familiar. The cartomancer must consult her harrow deck each day to prepare her spells and cannot prepare spells that are not stored in the deck. The spell deck cannot be used for this purpose if any cards are missing.

This ability replaces the witch's familiar.

While the ability to have it communicate with other familiars seems... odd, I think the option witches have to teach their familiar spells by treating a spell scroll with a special ritual would work just fine here, in a refluffed version.