Railway Sleeper Offcut or similar . . . . (Woodhall Park SN2)

I need just 46cm (18") of railway sleeper, or something similar, to re-fix my cast-iron 'village pump' to. The current piece of wood is 46cm x 23cm x 10.25cm (18" x 9" x 4"), but as long as it's a really solid piece of wood, I can get a larger piece cut down to the required size. Many thanks.