I found a source for the extremely hard to find 6 volt mini bulbs used in the old petal reflector sets which were popular from the 1960s to 1980s. These 6 volt bulbs are sold in a 5 pack with a flasher, under the Santa's Christmas Magic brand, item no 16990.
Imported by LB international, Hauppauge, NY 11788. The bulbs are 125 milliamp current rated or 3/4 watt so they are compatible electrically with the original bulbs. You'll need to swap out the original base with the petal reflector.
You should be able to find them at the local christmas store.
Update 12/01/09
Bought 2 more packs of 6 volt bulbs at another store and these are rated 90 milliamps or 1/2 watt! Go figure same brand, different spec. I guess when you're dealing with bulbs made in China, there's no telling what you will get.
Have a Merry Christmas!
J.S.P.