You can get it from the DLS. Start TS12 and select content. Put Harbour Master in the search box and select the multiplayer version (by Philskene I believe). Ideally you should have a FCT (First Class Ticket) as this will speed up the download speed by quite a lot. Alternatively you could type "multiplayer into the search box to see what other multiplayer sessions there are. You only need to drag the session to your download box, not the route.
