Who sells 4.8v regulators
You don't need 4.8, get a bunch of radio shack 5 volt regulators and put them in parallel and you can build a regulator as big as you need 4.8 isn't a magic number. 5 will work just fine, even on 4.8 volt rated servo's because they still have to deal with the over voltage of a 4.8 volt pack when it's fully charged.