I don't know for a fact but my guess is they were put on as turn signals. You should be able to get bulbs anywhere. If there are currently bulbs in the sockets pull one a take the number off of the base. If there are no bulbs in the sockets look to see if the pins are straight across or offset and if it's a single or double contact.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.