Let me share my google-fu with you:
Check health food stores, a quick google search for "herbs" in your area turns up Major Health Foods 1001 S 10th St. You might want to check there or anywhere that sells herbal tea ingredients.
There are a few online retailers that I know of, I have a couple links on my blog under "References and Links", one of which is Starwest Botanicals, they have a very comprehensive selection. They'll turn up in a google search for "bulk herbs".
If you look for things such as "sassafrass root" under the google shopping, you may find a number of stores such as amazon sell the same brand, google the brand and you'll find that the company sells direct.
I hope that helps.