buy the H5 V-brakes, and the mono coloured salmon R1 V-Brake pads as replacements.
the curvature for V-brakes matches up on 20" wheels no problem.
or, if you don't mind having to line up the pads each time you replace them, use the T1 in mono coloured salmon.
stay away from the dual compounds, they're not that good, despite being the same price.