The first post in this thread has the server connection information, and some links to where you can download my version of megamek. Right now, the most current package I've put together is 41.4-steveD which is within a revision of 41.4 official. You'll get a notice about client mismatch, but it's worked fine whenever I've had to use one with the other. As soon as I can get files from the sourceforge SVN server again (it hasn't been working lately) I'll be putting out a custom release based on the 41.5 code in progress.
But you don't need my version of megamek to connect to most of my server instances, the official packages will work as well, unless otherwise noted.