You can only get it from hitting other players opted into the pvp event. From what I've seen it seems like the mith drop rate is 1/75 or something. Hope that helps
It doesn't drop a lot from players, which is good cos it means demand for them is high, I would say Mith drops between every 50-100 attacks / steals though I've had 4 mith drops in a row before, I've also gone all weekend without a single mith drop.
I'd say the Mith drop is lower, around 0.5% (but who knows, they could be constantly tinkering). I *think* I saw Charlie write on a wall post that the chances of a Bomb drop were around the same as a Mith drop.
I could just be lucky (or unlucky), but the 1/75 seems right to me considering both how often I get/lose one.