Have you looked at http://glutenfreetraveller.com/tag/scotland/ ? You may have found this already, as it came up straight away on a google search. I have spent time in various of the places you mentioned, so am sure you will have a great time. (I don't have a gluten problem, though.) I love the area around Pitlochry - my aunt used to live by Loch Tummel, so spent many holidays up there.