I do not know how one would obtain it, but Ghrelin seems to be pretty powerful in treating PD. Here's an article:
Prolonged fasting, lighter meals, green tea extract, marijuana, and coconut oil all increase it. It works when taken orally. The MCT's in coconut oil increase its utilization in the brain. So it seems ending a long fast with coconut oil is a good idea, as well as marijuana and green tea extract during the fast.