I'm sure a google search will get you many leads on where to get vellum. The next thing is aging; lots of tutorials around the web, and here, for that. The burns take some practice to get right, just use a lighter and control the burn closely. The hardest part is drawing it out by hand after all of that setup work has already been done. If you draw then do the aging the ink will fade out too much because the aging techniques are artificial and we don't have time to sit around for centuries while the paper turns brown. The hardest part is learning to draw if you don't already know how. So I would practice a bunch on regular paper until you can draw things just the way you want and age them and burn them correctly then go get the vellum once you have gotten really good. This could take some time to achieve.