Is it possible to create an own MacPorts (proxy)repository/server? Is it possible to deploy MacPorts server on an own server periodically updating it from global one (i.e. create MacPorts distribution/update proxy server)? So that all computers within organization could access this server to install software and not the global macports server?

Is it possible with Homebrew, Fink?
You could probably in theory patch Homebrew to point to your internal Git server.  But it would still download the source for all the packages from their normal upstream locations.  You could bottle everything, but that would be a lot of work.  It don't think it would work very well.