There is an internet outfit selling old stock G.E. Merry Midget mini bulbs. They have several types, the bi pin base style in 12 volt for 12 light decorative sets and also a wedge base type for 20 light sets.
Go to
http://www.thecollegetoolbox.com/geelli.html for the main page showing various G.E. bulbs.
http://www.thecollegetoolbox.com/geelascopure.htmlfor 12 volt multi color bulbs. (12 volt yellow are now sold out)
These bi pin base bulbs are very hard to find. The price is great too!