The small bulbs are shown in the manual as Mazda number 82. Wagner part number is BP82. That is the industry number for that particular bulb. They are on ebay all the time, rock auto carries them as well. I could not find them on the NAPA site but they likely will have them as well.
http://www.ebay.com/itm/Westinghouse...-/230986442534 This guy's price is a little out of whack. Rock auto charges just under $1 each, and you could likley buy them from an auto parts store. They may be used in the larger 6 volt flashlights as well. The 82 has two contacts on the bottom.
I have always just used the headlamp bulbs that are available from Mac's. Although the carrier shows a single filement bulb, you can use the standard double filament (hi/lo) commercial bulb and wire it appropriately. Which wire would be ground should not matter, since the terminals are isolated form the base.