Zz: Basic statistics. There are a finite number of particle types, and a finite number of particles in a human-mass object. Therefore, in an infinite universe, any possible combination of particles in such a mass will have to reoccur.
If our universe is infinite, and the "missing" antimatter is elsewhere in the universe, then there has to be an infinite amount of it. Thus, any possible combination can be found there.
If the antimatter is not in our universe, but segregated into a "mirror" universe, and that universe is infinite, then the combination can be found there.
If our universe is not infinite, then it is possible that there are more possible combinations than particles to make them, and there is no guarantee that a given combination can be found.