There is a new biography of Park entitled "Willie Park Junior" published in England by someone named Stephens. I think someone posted a review of the book a while ago. I ordered it a few weeks ago and it hasn't shown up yet.
As to his drawings or other materials, I have not uncovered much at all in my research at Olympia Fields. One drawing of the North Course that may or may not have been done by him, and only a very few construction photographs or early photos of the course. Almost nothing that shows original greens aside from video from the 1928 U.S. Open that shows 2 greens that look similar to what I see out there today (holes 9 and 16). A great picture of one bunker on 16, which also looks similar to the bunkering done before the 2003 Open. Also, there is an article from a newsletter in 1924 or 25 showing the greens construction, with a drawing of the various layers. All in all, very small beer.