I ordered my leaves on amazon (http://www.amazon.com/dp/B003DKG418/?tag=skimlinks_replacement-20). It's a little bit expensive, I think I paid $11 for one ounce including shipping.
It's great for experimentation, just make sure you understand the risks associated with safrole. Some people get...
This weekend, I gave a shot at my first non-extract root beer. I used the 1912 Fleishman recipe (http://www.root-beer.org/recipe2.htm), adjusted down for just one gallon. Through a bit of a mishap (my brain focuses more on prices than an details sometimes) I ended up with sassafras leaves...