Bob Ross® Dark Sienna Oil Paint
Bob Ross® Dark Sienna oil paint is another fundamental oil color used as part of the dark base mixture for mountains, rocks, trees, and more. If you paint often, the 5 oz tube will be the way to go, otherwise, the 1.25 oz tube should last you quite a while.
If you cannot find a local retail outlet for Bob Ross® Dark Sienna then you might consider buying from a reputable, high-volume art supply dealer online. The normal list price for the 5 OZ tube of Dark Sienna is $17.49 and the 1.25 OZ is listed for $7.29 but you can buy it online for far less. The buy link below doesn't commit you to buying but will take you to the merchant website where you can see what is available.