Loch Borralie (the largest of the Durness Limestone lochs) has (had?) a good head of Char. We used to catch them just off the island with a Hi-Di (or equivalent) and a flashy lure like a Goldie. Given all the changes up there I'm not sure how you access the fishing these days but I'm sure others here will know.
In general almost all of the West Highland lochs that have salmon cages on them have a good head of much larger Char (and Brownies) thanks to the pellet diet.