Post on master, read on slaves?

I used multisite to create subdomain sites for every beach on the east coast of Florida. Each has their own domain name. Each beach info site has its own custom content. But I also want general announcements I post on my master (surf shop) site to automatically appear on each of the slave sites (for each beach). It would also be cool if the photo from the most recent general post could always be included as one of the images included in the slider on each slave. Any advice on making this a reality would be appreciated.