Bramley, I've still got a couple of Makita ones about that age. I have more recent drills, but it's such a shame to throw the old ones out.
I get the old type Ni-Cad 9.6v batteries from one of the Ebay shops.
Try there.
A long shot............... I've never done it, but a friend of mine simply dismantles the battery case, and replaces the re-chargeable batteries inside. He seems to have no trouble. They are usually just a few standard size batteries taped together.