Ocica is the last set of story map currently in the game.
It refers to the city of the same name on the overworld map.

They have a 0.5% chance to drop 5* emblems or a 5* star tank
(the tank is from a limited subgroup, it is not rolled against all 5*).

So on average you'd need to do 200 Ocica to see one of these "Jackpot" drops.
That may seem low but it is extremely generous that the drops are in the game at all.

The slight catch involved is that if you can beat Ocica you are "done" outside of PoC. If you can farm it, then you are simply stockpiling.

The rewards should be seen not as "hey I can get this" but as "this is ABs way of saying thanks for sticking around while content is being made for the next push" (which are event(s?) if the discord chat is anything to go by).