There are several highly-respected contributors on this Forum that also maintain excellent blogs with articles that may be suitable (though perhaps too lengthy) for your bulletin. Off the top of my head (at the risk of excluding other worthy contributors) I can think of Phil Vatz and Church Militant. Look them up here - their signatures point to their blogs. They may agree to allow you to freely republish their material (with attribution, of course, which you should insist upon even if they don’t).
The length of the blog posts might be a problem. You may find it necessary to edit them for space constraints, and this might not be acceptable (I wouldn’t want someone to edit my work). However, if you ask nice, some nice blogger might agree to provide a shorter version of some posts. I don’t mind cutting my own content, but I would not want someone else to do so.