I don't know how relevant or not this is but I assume there is a connection with the village of Butterstone which lies between Dunkeld and Blairgowrie. There is also a Butterstone Loch which I have fished many times. You are certainly in the right vicinity as the Duke of Atholl had lands around Dunkeld and built a dower house there (now the Hilton Dunkeld House hotel). What Matt says covers the subject as well as you can get I think and I am sure if your family came from Atholl lands they would have had allegiance to them. It is as good as you will probably get for a clan association. None of them are that particular anyway unless it is one like the Buchanan Society where they actually give money away to clan members so are a bit fussier. If you are paying them cash they are a lot more accommodating!