There are a few descriptions of /proc round the web, a fairly good one is at
You are perhaps specifically looking for procinfo, which is usually in /usr/bin.
If you want to look at the source, then download a source source rpm and install it. By way of example one can be found in http://fr.rpmfind.net/linux/freshmeat/procinfo/
Install it with rpm -iv, when it will appear in /usr/src/REDHAT/SOURCES, decompress with bzip2 -d, then extract the files with tar xvf.