@ChaHarper There's the substantial remains of a building with many of the features of a broch, including the hollow centre, and the double walls and apparent accommodation within them, but roughly rectangular in plan, at Castlehaven Bay near Borgue, in Galloway. Whether it's a related to brochs or not I'm not qualified to say.
@simon_brooke Thanks for telling me it existed...I found the entry on Canmore:
https://canmore.org.uk/site/63623/castle-haven That doesn't make me qualified either but I trust Canmore to be filled with facts rather than opinions...