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This is the forum for Pathfinder Society Organized Play GM questions (questions about specific published scenarios or General PFS campaign rules). I've flagged your post for movement to the "advice" thread.
Having said that, the easiest way to accomplish what you want is to simply do it. Use the stats for the Android race from the Iron Gods player's guide. Give them NPC stats as suggested by the core rulebook. Give them a "jackhammer hand" statted as you want as a natural weapon. And then just give them a level of monk. Since you're creating the race, feel free to give them a special ability "The hammerdroids can make a flurry of blows with their jackhammer arm, but may not flurry with any other weapons."
Be careful with the stats on that weapon. A x4 weapon is always a dangerous thing to put in a level 1 encounter as it might take a character from fully healed to outright dead in one hit. I'd recommend either holding off on encountering them until the characters reach level 2 or 3 or creating a "run-down" version whose weapon only does x2. You can then introduce the x4 (maybe using elite array stats) at a later level.