  The stochastic $R$ matrix for $U_q(A^{(1)}_n)$ introduced recently gives rise
to an integrable zero range process of $n$ classes of particles in one
dimension. For $n=2$ we investigate how finitely many first class particles
fixed as defects influence the grand canonical ensemble of the second class
particles. By using the matrix product stationary probabilities involving
infinite products of $q$-bosons, exact formulas are derived for the local
density and current of the second class particles in the large volume limit.
