Two are sold by Tars the arms dealer on the second floor of the apartments (10,000 credits each).
One floor down from Jensen's apartment, you can find a Praxis kit inside a stash hidden in the floor of the unit with the eviction notice on the door. Open the level 3 locked safe to get the kit (Passcode: 5555) There is another located in Koller's Dungeon - locate a moveable painting by the elevator hiding a vent leading to a gassed room.
