There is another thought. Why not research what gypsies and other Travellers wear today in Scotland? Or, if they are not usually kilted (and it is very likely that they are not, if ever), you could research back in time until you come across tartans, kilts or other distinctive dress that they wore---probably a couple of hundred years--- that appeals to you.

The Travellers' culture is still alive and well in Britain. I have a friend whose mother grew up in it as a child. She speaks Rom fluently, and he knows a bit of it himself.

You see, the idea of clan tartans as we understand it didn't come about until long after the clan system had vanished, and long after its successor, feudalism, had also vanished. It was for the most part invented by mill owners, cloth merchants, tailors and others in order to make money off the vanity of the newly affluent bourgeoisie enriched by the industrial revolution in the early to mid 19th century.