Well, I can only speak for myself, however, after an extensive 9 years of formal study, I really have not found the studies or gestural drawings of some of my favorite artists. I must admit it is from lack of looking, however, if you are looking for a Master painter and cannot find their Drawings, I would suggest the following:
Try that “Old Master”, if you want to find what you are looking for most books in print only scratch the surface of a particular Artist’s work. It is the case frequently that a conglomeration of books of high-quality images would do the trick, yet if you are an Artist, you know this is a bit of a mystery as they could be privately held or not exist at all.
Study and Draw from the Paintings...study the compositions and lighting and invert colors to value studies...it is like taking our training and reversing it, depending on your level of study as these Master studies can be difficult to find, if they exist for view to the public, or if a Painter ever created Drawings that were published. They may exist in Museums or Collections and are kept from view to the average person. Private Museums exist, museum & private collections, who simply prefer to preserve the works and they may be periodically shown or you may have to be a “super-art-sleuth” to figure out where these works are.
As an Oil Painter myself, the least fun part of the process for me is the process. I can draw with my brush. Yes, I had to learn how to Draw and from Objects, Animals, People, Architectural structures, understand Perspective, and some Outdoor Scenery. But, my favorite part is just Painting; not necessarily Drawing as I have a plan in my head. Planning with Drawing and doing Color Sketches will make the entire process faster, yet the energy is not the same. They are two different approaches to the Final Artwork.