They don't exist, as far as I can tell; all psychic-casting classes are spontaneous. Even prepared-casting classes that switch from Divine- or Arcane-casting to Psychic-casting through an archetype (like the Mind Blade Magus) automatically become spontaneous-casters. Below are my thoughts to justify this design decision based on my own perceptions of the fundamentals of casting. This is all flavor, and not based on mechanics of a game, but instead on "real-world" applications of those mechanics, as they would be seen in the universe of Pathfinder (not specifically Golarion).
If I had to guess why, I'd say that this is because Psychic magic - by its nature - is innate, like that of a Sorcerer. So first, I guess I need to establish the fundamental difference (as I see it) between a prepared-caster and a spontaneous-caster, and how they cast their spells. Wizards study the laws of nature and physics and memorize complex formulas and words of power in the form of spells. When a Wizard casts Fireball, he's NOT pulling power from the depths of his being, coalescing it in the palm of his hand, and warping its molecular makeup to match that of the element of fire (that's what a Sorcerer does). Instead, he's exploiting tiny cracks in reality - imperceptible pockets of potential energy tucked between the threads of space and time - using words and gestures of power that, when used in concert, break open these cracks in a way determined by the specific gesture and word that shapes the energy into a desired effect. The Wizard is merely molding and aiming an energy that is otherwise not a part of him. As with prepared divine casters, they simply beseech their holy patrons, who essentially do everything i just described a Wizard doing for the caster. A Cleric or Druid merely needs to utter a few words as a divine request; no gestures are needed. An Oracle is essentially the same case as a Sorcerer, except instead of being infused with energy from the universe itself - or at least with power from a creature who in turn draws energy from the universe itself - an Oracle is infused with energy from a Divine patron.
So what does this mean for Psychic casters? Well, as I said - by its very nature, it's innate. Psychic Magic is literally a manifestation of the caster's own ego, emotions, or some other facet of their personality or self-identity. The closest any Psychic caster comes to being a prepared-caster is the Occultist, who must sync himself with one or more objects of psychic significance, but even then, the power is still within him. The objects are more acting as batteries, powering different components of the magic within him. The Medium is a bit of an odd beast as well, but keep in mind that the only magic he can cast that's Psychic magic is also the only magic he can cast without assistance from outside forces.
So here's my conclusion: all prepared casters are so because their magic is coming from outside sources; they simply aim it. With this in mind, the moment a Psychic caster must prepare his spells is the moment he's no longer a Psychic caster, because even if the magic is still fueled by emotions and thoughts, the magic won't be coming from HIS emotions, or HIS thoughts. Instead, they'd be coming from the emotions/thoughts/whims/etc. of what would fundamentally be the caster's patron, which would fundamentally make him a divine caster.
If I had to guess why, I'd say that this is because Psychic magic - by its nature - is innate, like that of a Sorcerer.
I skimmed the possible disciplines for a psychic in Occult Adventures, and, yes, for them it seems to be mostly correct. The only oddball is the faith discipline, where the caster probably gets their power from a divine being.
It might appear so, but I think the fact that it's called a Discipline is more telling. In the case of a Psychic of Faith, it might be the constant praying and religious practices that are granting him his powers, but the source is still from the caster. There's no actual connection between the Psychic and his deity any more than there is between a Commoner who prays to the same deity. It's the discipline of faith that hones the Psychic's powers. Waking up every day and paying homage to Torag by lighting incense and meditating clears his head and gives him inner peace. That inner peace is how he taps into his own psychic powers.
Wizards can take an arcane discovery to prepare one whole (Wizard) spell for psychic casting at significant penalties/limitations.
Psychic Preparation (Magic Tactics Toolbox pg. 3): You have learned a limited way to access psychic magic (Pathfinder RPG Occult Adventures 144). When you first prepare your spells for the day, you can prepare one spell as a psychic spell. This spell must be at least 2 levels lower than the highest-level wizard spell you can cast, and takes a slot 1 level higher than the spell’s actual level. When you cast this spell, it operates as a psychic spell, including using emotional and thought components in place of somatic and verbal components, and only having expensive material components.
Hmm. Well, that's...Arcane magic is fickle, and...uh, solar winds...COLOR SPRAY!
There is one way to play a sort-of prepared psychic caster; an Arcanist with the blood arcanist archetype who picks the psychic Sorcerer bloodline for said archetype.
There is one way to play a sort-of prepared psychic caster; an Arcanist with the blood arcanist archetype who picks the psychic Sorcerer bloodline for said archetype.
Good catch! Shame about not getting the spell list and the useless 9th level bloodline power, though.
Note: Psychic magic specifically taps external sources for power (see Kineticist and Spiritualists getting their power from the ethereal, Mediums and Mesmerists getting their power from the astral) getting their power from the astral, rather than arcane which tends to tap into things like your bloodline or your race's innate abilities.