Currently I would simply like to find all files that have not been modified in the last X days but ultimately I would like to be able to make more complex queries against my sub
As already mentioned, svn log/info can be combined with shell commands to find what you want. Alternatively, you could directly use SVN's own API in C/C++ to programmtically process repository enties. SVN has Python bindings. If Java is your language of choice, try http://svnkit.com/