mkocal,
If you have one, just pull it and take it to the autoparts. They should be able to hook you up. There should be a number printed on one side of the base. Try to match it. You don't want too high a wattage, as it will make your blinkers flash weird. I don't think you have to worry about the bulb getting too hot, as it is flashing, though.
If you don't have one, ask again, and we'll see if we can't scrounge a # for you.