Primary Distribution Point
You might want to read the build instructions for inspiration on where to go after downloading the source.
The bindings for perl, tcl, ruby and python are part of the rrdtool distribution. Here is a list of others:
RRDtool source is stored on GitHub and this is also where development happens. Just fork the repository, make changes and send me a pull request.
Note that the version number in the header of the source files you get from github may be 'off' this is because the version number gets set by the release script prior to building the archive.
When building from a git clone, run