  The intertwiner of the quantized coordinate ring $A_q(sl_3)$ is known to
yield a solution to the tetrahedron equation. By evaluating their $n$-fold
composition with special boundary vectors we generate series of solutions to
the Yang-Baxter equation. Finding their origin in conventional quantum group
theory is a clue to the link between two and three dimensional integrable
systems. We identify them with the quantum $R$ matrices associated with the
$q$-oscillator representations of $U_q(A^{(2)}_{2n})$, $U_q(C^{(1)}_n)$ and
$U_q(D^{(2)}_{n+1})$.
