What you need is called a single-pole, double-throw switch. It has to be rated to handle the headlight current, and I'm not sure what that is. I've measured it on my Porsche as 9 amps for the low beams and 11 for the high; Spridgets with sealed-beam headlights are probably about the same. So, you'll need a switch rated around 15 amps DC, for margin, and I don't think you'll find this in a simple, small toggle switch. You might find one rated at 15 amps AC, but that's an entirely different story--a 15 amp AC switch won't handle anything remotely close to that for dc.
So, this would be a good time to add relays to the headlights. Then, your switch handles only the relay coil current, which is only a couple tenths of an amp. As an added benefits, you'll see a real improvement in headlight brightness and your light switch will last longer.