I need to find a 12 to 6 volt reducer?

This reducer is not something that I've ever seen - I suspect someone out there must know where you can get a step-down transformer but I'm not sure about putting that is series in a n autoomotive electrical system, since it could fry everything if it were to burn-out or short circuit. I strongly recomend either changing the whole car over to 12 volt or getting another 6 volt battery. Regardless of whether they seem to last long enough, they operate engine starter and all accessory items the way that they should. If you go full conversion (I did on a '64 Beetle) it's a lot of work but the whole car worked perfectly when done. You could add a second battery in parallel which keeps you at 6 volts but boosts the amps to give some longer life but as I said, I think stick to status quo and buy a battery as needed.