I've been churning out assassins and trying to assassinate (with precious little luck), but still no Assassin's Guild after over 120 turns. I don't think this strategy is doable without one, since there's only like a 6-9% chance of succeeding in any assassination (other than 0 level diplomat, but good luck finding one of those). Even if you get lucky, the next attempt with that assassin results in him either dying or losing that one point he got through ineptitude.

And I have yet to get any points from sabotaging. It's fun, but there's nothing happening in the traits, no matter how much I blow up. Are you playing a modded game?