Hi, I don't know about your Speir but I have folks with the last name Speirs (interchangable to Speir) in Ayrshire. I have looked at my tree and it seems that for a while they were in Tarbolton, and prior to that Ochiltree.
There is a story in my family that the surname came from some sort of French nobility who escaped France and ended up in Britain, slowly travelling up to Scotland. He took the surname Speirs from the first person he met after getting to Britain.
