LEGO Mindstorms 9797 (NXT Education base set) Software Download
I contacted Lego and they gave me this link for a PC: 

https://fileshare.corp.lego.com/node_share_links/119233?token=7a9527d5-cd94-491c-88b3-689587eae5ae
I don't have the link for a Mac, but you can ask Lego for it.