Hi Kurt,
the code files (with the extensions *.h and *.c) are all below those Makefiles, right in the main directory of the github repository that you linked to. In order to proceed with the RAxML installation, simply click the green "Clone or Download" button on the upper right part of the page, then download the zip file. If you extract this into a folder, you will (hopefully) find all the files that you also see on the repository page (Makefiles, and source files). From then, follow the instructions as given in the README.
Lucas