Have a look at the Wiki about possible plant sources. Also use the search function about plants and possible extraction routes.
Generally the best results you would probably get with Virola Theiodora resin. But it's hard to get nowadays and there were quite some reports about its unethical sourcing.
69ron posted his preferred tek for it (but his results are debated by some users here, as he played a shady role in the fake-THH case):
* boil in water and bring the pH to 4 using citric acid.
* filter out plant material.
* defat 10 times with DCM.
* bring the pH to 9 with sodium carbonate.
* extract with DCM 5 times.
I claim not that this is the truth. As this is just what got manifested into my mind at the current position in time on this physical plane. So please feel not offended by anything I say.