Subscribe on the Back-on-Track mailing list. A lot of relevant stuff is distributed here. See what to do. Actually the two newsletters below is also distributed via this e-mail list.
Rail Report Europe is a magazine on night trains in English, but also about other cross border stuff, issued on a quarterly basis. It is edited by Trevor Garrod and Jochen Reitstätter. See first edition here, where you can also subscribe. Find here the second edition.
Night Train newsletter is a newsletter in both German and English edited by Joachim Holstein. Add your name to the mailing list.