If you are like me you are either pissed that A: you cannot by lockpicks in shops easily. or B: alchemist shops dont carry the poison you need. well i found a shop that solve both. It has been a while since i went here so its a little fuzzy but i should be able to remember a lot. Go to the waterfront district, then go straight to the wall of the city. Walk very close to the wall and you will see a man in black. Talk to him to buy any thief stuff you need. (I think he is only there during a certain part of the day, im not sure what. srry.)