Hi Mongo! I've never heard of nor seen a Madrid newsletter in English. You could likely get one from one of the newspapers in English giving you the day's headlines but it won't be geared towards tourists. Sounds like something which could be quite useful but no doubt a lot of work to put together each week/month. Would you be interested in Spanish-language sources? Because there are LOTS of websites on Madrid in Spanish which cover touristic or "fun stuff" going on like http://www.guiadelocio.com which covers not only Madrid but most of Spain's cities.

Good luck and have fun! Saludos, MadridMan