Whats a good web site for free MSMTS add-ons?
Alabama Railfanwww.alabamarailfan.com
More than you can imagine. You just have to be patient unless you want to pay. The biggest clue. If there are a bunch of new routes (like now) in the new files, you are doomed for a couple of weeks. Also check the links they have. You would be amazed what is out there. The UK version of Train-sim is easier to get a download, but you basically stand in line waiting to download a file.
MLT had a link to a download site, but it disappeared a while ago.
Alabama railfain is good too. Some of the payware sites have freebies. And don’t forget the Canadian Pacific Railroad site. They have a bunch of stuff for MSTS, including part of a route (demo of Kicking Horse Pass).