You might find some info here:
http://www.trout-fishing-scotland.com/
It should give an idea of what you can find, and look further for the place that interest you. I haven't fished that far north, but that part of the country is my favourite and I think the more scenic by far. And if you go after May, bring some insect repellent, if the midges are out you can't be outside, especially in the evening, without becoming crazy ...