ok so I thought I would resurrect this thread as I have just stumbled upon an interesting development.  There is a native Australian plant that may have workable levels.

Acacia complanata, generally known as Long-pod Wattle and Flat-stemmed Wattle, is a perennial tree native to Australia. It can grow 5–6 m tall, but more often it grows as a large shrub. It is not listed as being a threatened species. It is commonly used in environmental management.

The major base is Nb-methyltetrahydroharman, isolable to 0.3%, but there are also trace amounts of tetrahydroharman and N-methyltetrahydroharman.