I did a bit of research and found that Litsea cubeba is also known as ... Dieng-si-sing, Earking, Entsurem, Jayar, Mang tang, Mejankeri, Ser-nam, Sernam, Shan ji jiao, Siltimur, Siqbil, Tanghaercherkung, Terhilsok and Zeng-jil. I looked each one of these up and aside from finding sources for the essential oils (apparently used extensively in Ayurvedic medicine) could find no source for any of them. From the descriptions of the taste, however, I thought you might like to try a substitute. The fragrant sumac, Rhus aromatica, produces tons of small red berries coated with very tart malic acid. The seeds inside are hard and a bit like black pepper, so that when the berries are dried and ground, they taste a lot like lemon-pepper. They have been used for centuries as a spice in middle-eastern dishes (although it is a different species of sumac that they use--I think it is Rhus coriaria). If a tart, peppery flavor is what you are after, this is a great substitute and best of all, it's an easy to find and grow, hardy
native plant. It is also supposed to be really good for you, so it's a win-win.
Shape.com (By the way, all the sumacs in the genus Rhus are edible. They
should not be confused with poison sumac, which is Toxicodendron vernix, a relative of poison ivy.)
Here is a good photo of the native variety, Rhus aromatica ... It makes great "lemonade" as well as a spice. (Tastes like a combination of lemonade and cranberry juice.)