Tons of great content available from the Olmsted Bros archives. I use their flickr account to find stuff, including great numbers of Plans, Photos, and planning documents.
https://www.flickr.com/photos/olmsted_archives/If the Olmsteds worked on the the land planning for a course, you can find it in here. Obviously even more non-golf stuff in there as well. They worked on ANGC, Fishers Island, Merion, Pasatiempo and many more.
It can be a little finicky to use, you have to use the proper specific search button to search only their account and a few other things like that, but what they have is pretty spectacular.