  We obtain a classical spin liquid (CSL) phase by applying a magnetic field in
$J_1$-$J_2$-$J_3$ Ising model on a kagome lattice. As we proved in the previous
study [Phys. Rev. Lett. {\bf 119}, 077207 (2017)], this model realizes one
species of CSL, the hexamer CSL, at zero magnetic field, which consists of
macroscopically degenerate spin configurations with mixed total magnetization,
$M$. The magnetic field selects its subset, which can be mapped to a trimer
covering of the dual lattice, and forms a magnetization plateau of $M=1/9$. In
addition to this CSL, we find two other magnetization plateaus at $M=5/9$ and
$17/27$, which are ascribed to the "multimer" superstructures on a dual
lattice.
