Whittaker mentioned these resources a year ago, but if a week is a long time in politics, then what is a year in a Higher Education institution?!
The National Library of Scotland's Glen Collection is an invaluable source of early Scottish song and other music. It has been digitised on the Internet Archive. Here's the link. (If you forget it, then you can go to the Internet Archive homepage and search on nlsmusic).
Additionally, the NLS has started digitising its own scores for itself - there's a page for their Digital Gallery; scroll down to Early Books of Scottish songs, like this:-
 | Early books of Scottish songs Three early books of Scottish (and some English) songs with melodies and illustrations. Includes songs with words by Allan Ramsay. |
