I only spent a few minutes searching around for something that might work. It appears there are a few packages that may do the job and build a local mirror of the repositories: apt-catcher, apt-proxy and apt-mirror. Here's a howto on creating a proxy and this one for creating a mirror.

I don't have a linux machine handy right now, but I'd bet the apt-mirror would work.

I like the idea and if it works we could actually create a single master repository for packages that could be hosted at several different locations for speed and availability.