Leading is a lost art. The best advise I can give is to ask custom shops in your area if there's anyone versed in leading. The reason lead was used back then was because it was the best material for that purpose that was available at that time. Modern plastic fillers should do the job just as well. Wanting to use original materials is an admirable idea but few do it anymore. Good luck with your quest.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.