After searching extensively, I couldn't find Exchange Server 5.0 anywhere, but I did have the Evaluation version on hand, so I made ISO's of them and here you go. Hopefully somebody out there has the retail version and this will inspire them to upload it.
From the CD case:
Evaluation License for Microsoft Exchange Server 5.0, Microsoft Windows NT Server Version 4.0 , and Microsoft Outlook 97.
The Software is time sensitive and will not function upon expiration of the 120 day period.
4 Disc Set includes: Microsoft Windows NT 4.0 Server - 120-Day Limit on Use Microsoft Windows NT 4.0 Service Pack 2 Microsoft Exchange Server 5.0 - Evaluation Software 120-Day Limit on Use Microsoft Outlook 97 - Evaluation Software 120-Day Limit on Use