FYI:

"Venice Turpentine
Genuine Venice turpentine is collected from larch trees. It is a viscous liquid resin; such resins exude from certain trees and are often referred to as balsams. Venice turpentine has been used in painting for centuries and has excellent handling and aging characteristics. It should not be confused with the thinners gum turpentine or rectified turpentine. Venice turpentine is used as an additive to thicken other media. This resin is popular because it gives body to the paint film while maintaining gloss and brilliance, and it yellows very little over time. Genuine Venice turpentine is not easily found and some companies are using a substitute resin called Canada balsam. Canada balsam has two advantages over Venice turpentine-it dries more clearly and it takes only one or two hours to dry, as opposed to three days for Venice turpentine. However, Canada balsam has a distinct disadvantage in that it is more fluid than Venice turpentine."

Originally only exported from Venice, hence its name. Some now produced in Switzerland.

Several art supply stores carry it. Google for it and you'll get multiple hits.

JC

"...it is always advisable to perceive clearly our ignorance."ť Charles Darwin