There are more than just those few, there's the likely stone circle (often referred to as cairn remains) by the Edderton Stone, Douglas Scott also indentified another possible a few km along the road I think which I've yet to find, there's possibility of one or two destroyed around Dunrobin, Bridge of Broubster, Backlass, Auchinduich by Lairg, Dailharraild / Clach an Righ, Learable Hill, there are others too...

One thing I do keep reading is about possible circles that get lost in forestry - and I wonder if you plant trees you loose a circle, esp an already damamged one, in or to trees a lot easier than a cairn. Lot's of cairns still traceable in woods, but I can't think off top of many standing stones or circles known amongst trees around here...

The circles we do know tend to be of quite modest stones. I personally recon we've lost quite a number. But I agree it's definitely not stone country like the likes of other areas.