Replacement taillight lens is a Peterson 420-15, it is still sold today although post mini bike era lenses had to start having DOT approval or meet standards and the newer lenses got script on the bottom that the older ones did not have. they can be found for about 5-10 bucks, should be able to get them at even Napa or a well stocked trailer supply store.
Gotta be careful, someone on Ebay made copies of an original Bonanza spare parts tag for one, throws a new lens in a baggie, and staples the tag to it making it appear to be a NOS one......it is not, the DOT 1975 script on the lens kinda gives it away :facepalm: there are a few period correct ones to be found, but they run about 35 bucks usually for them NOS.
All the headlights and kits I have had used the GE 4420 headlight bulb.