Hi, Dave,
If you have access to transport, anywhere with a coastal view along the A861 from Glenuig to Loch Ailort, and then the A830 from Loch Ailort past Arisaig to Mallaig can yield Great Northern Divers. *NOTE* On leaving Arisaig on the way to Mallaig, just as you're leaving Arisaig, turn left on to the old coast road which will bring you back to the main road at the sands of Morar.
You could also try the short Rhu road west out of Arisaig (a dead end - you must return the same way), which offers good seawatching for divers, grebes, ducks etc. Don't ignore any freshwater lochs in the area - I have seen red-throated and black-throated divers on them.
Ferry crossings in the area - e.g. Mallaig-Armadale (Skye), Kilchoan (Ardnamurchan) - Tobermory (Mull), or, if you have a whole day to spare, the Small Isles vessel which sails a round trip from Mallaig to Rum, Eigg, Muck, Canna etc., can yield good seabirds, including gannet, Manx shearwater, razorbill, guillemot, Great Skua and so on. Note that this is dependent on what birds are actually present at this time of year, and Calmac Ferries' winter timetable! Weather too, I guess!
Best wishes,
Dave Kennedy