|Daedalus the Dungeon Builder|
Though it's technically not spell casting, the Pathfinder Chronicler lets you whip out low-level magical potions and scrolls (with bonuses on using said scrolls) all day, as long as you have the gp. Not ideal, but it is another option if the goal is to simply "have access to spells" as opposed to "have a caster level." What purpose are you wanting spell casting ability for?
It was mostly curiosity. Back in 3.5e I had a fun (if odd) archer multiclass build that dipped into Assassin (and Rogue, Fighter, Ranger, Shadowdancer, Horizon Walker and Eldritch Knight), and I was seeing if it could be ported over to Pathfinder.
Paizo removed the Elf or Half-Elf restriction on Arcane Archer which would have been worth a 2 level dip to shoot Obscuring Mist or Darkness arrows from the Assassin spell list, but without a spell list there isn't really much point. Red Mantis Assassin is melee focused by default, so it's not an appropriate substitute. Probably a Magus dip is the closest fit, but it's disappointing that Paizo decided to deviate so radically from the 3.5 edition Assassin prestige.