Sharing Media Files in MU install

I have the web sites for 3 radio stations owned by the company I work for on an MU install.

I need the ability to create a "public media gallery" where images, audio and video can be shared among "selected" sites.

Right now we're having to upload everything multiple times (once for each site) and so there are multiple copies of the same files.

I've been searching WP and Google for a solution, but none so far. Just checking to see if anyone else found one.