If you click on "Trade skills...By Trade" in the box to the left, it will give you a list of everything a particular profession can produce. Beneath each product will be something like <Plans: ...> if they are not obtained directly from the trainer. Clicking on that link will tell you where the plans are sold or where they have been dropped. The ones in white are all sold by vendors, and it's possible that with the 2.0 updates, some of the green ones may also be sold now. Ordinarily, the green, blue, and purple ones are either drops or obtained based on rep from faction vendors.