Bob Ross® Phthalo Green Oil Paint
Bob Ross® Phthalo Green oil paint will be one of the less frequent oil paints you use. If you paint often you'll probably want to have a 5 oz Phthalo Green tube, otherwise, the 1.25 oz Phthalo Green tube should last you quite a while.
If you cannot find a local retail outlet for Bob Ross® Phthalo Green then you might consider buying from a reputable, high-volume art supply dealer online. The normal list price for the 5 OZ tube of Phthalo Green 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.