I do enjoy playing mandolin but I didn't bring it and I really never learned any Scottish songs.
Being a mandolin player myself, I can see why. There are a lot of good Celtic songs out there, though most of them tend to be fiddle tunes based on Irish music. The Scottish-based ones seem to be hard to find.

You can find a whole bunch of mandolin tunes here, though. Some of them are specifically labeled as Scottish. Surely you could find something appropriate there?

Any tune will sound good as an instrumental if you play it fast enough.

I'm no help with the cittern, though.