JungleBox is a great local source, but I usually collect my own. Its not too hard to find magnolia trees and oak trees here in SoCal. Magnolia leaves I gather individually off the ground, for oak leaves I usually bring a small hand spade and a plastic bag. The magnolia leaves get a rub down in warm water and then 3 minutes in the microwave. The oak leaves get rinsed in a colander, boiled for an hour and then microwaved.
It would be a huge pain if I was trying to prep enough to sell, but its not so bad for just my own needs. I still sometimes buy from Dane though.