Itās very rare. I only see it like once every 20 games, if that.
Yeah, according to Lauraās spreadsheet Thorās Hammer only has a weight of 0.1 regularly and 0.2 in overpowered. (A weight of 1 seems to be the default used, and the lowest weight is 0.05)
Without taking into account which drops are considered good, bad, or neutral (This plays a role in the probability which Laura was unable to share with me, so the true odds are still a mystery for now), the probability of getting one from a lucky block is around .02677% However, this estimate may include some drops which are Java exclusive, or some drops that were previously in the game but got removed (ex: villager tower, 9 chickens)