
Hello, I have one of those lamps too. They're lovely. I would suggest taking the lamp and/or shade to your local print shop where someone who is familiar with paper types can advise you on where to purchase similar material.
You'll probably have to take the original shade apart to make a pattern with it, but again, ask what kind of glue or tape (or staples) you can use that won't come apart or be dangerous in the heat.
Good luck.