I bought a turn signal switch from Golden States Parts. $18.95. I had already installed a wiring harness from Chevy Duty, which includes all the turn signal wiring other than the switch. Very simple installation. If you haven't converted your parklamps and tail lamps to accept a dual filament bulb, you may want to consider it as it makes a very neat installation.

The switch is chrome plated relatively small and looks right at home on the AD steering column.