question for someone who really knows Classical literature

I've been running into a bit of a wall with Hippocrates and Galen.  Many sources say that their works include large pharmacopeia or materia medica - lists of herbs and their uses.  

Of the works of Hippocrates, I've read (although I admit to skimming a few), On Airs, Waters, and Places, On Ancient Medicine, Aphorisms, On the Articulations, The Book of Prognostics, On Fistulae, On Fractures, On Hemorrhoids, On Injuries of the Head, Instruments of Reductionm The Law, The Oath, Of the Epidemics, On Regimen in Acute Diseases, On the Sacred Disease, On the Surgery and On Ulcers.  While their were a few brief mentions of herbs and their use in those books, most were in the appendix of On Regimen in Accute Diseas, but nothing like the "200 herbs listed by Hippocrates", often reference by other writers.  

Of Galen, I have read the Loeb Classic series, which includes his philosophy of medicine, gruesome experiments, arguments with other physicians and many and varied musings on many things.  But again, I am not finding the "large materia medica fo 400 plants" (or so) that is often cited.  As I understand it, "On Simple Medicines" only exists in one copy that has not been translated yet from Syrian (?).

So, what am I missing?  Does anyone know if these often cited works still exist, and if so, under what titles?