Bosch and NAPA have internal resistance coils. Search here for part numbers or ask here for part numbers.

One advantage of the external ballast resistor, is that you can easily wire the starting/ignition system to allow full 12v while cranking/starting and reduced voltage while running.

If you are using a foot-actuated starter, a special starter button is used on the starter, if you use a ballast resister.

I think you will want a 12v flasher. If you will change to LED bulbs, you'll need a special flasher.