The first harmonized psalms were published in Scotland in the sixteenth cemtury and there was probably a version in print continuously from when Andro Hart produced one at the beginning of the 17th century.

It wasn't unavailability of harmonizations that prevented most Scots from singing them, it was ideology. The Covenanters and allied extreme Calvinists disapproved of all elaborated religious music and would only tolerate single-line melodies in psalm settings.

Changes to this status quo were only imposed by the elite with the aid of extreme violence. Charles I's attempt to introduce a more elaborate Anglican-style liturgy in the1630s set off a civil war.

Sir Archibald Grant must have been one hell of an aggressive cultural imperialist to attempt this. He could not have done it without forcible evictions to eliminate tenants with Covenanter sympathies. (Perhaps he replaced them with Episcopalian Highlanders, as part of the settlement of Jacobite issues after 1784)?

Remember "new and far-sighted farming methods" really meant "booting your workers off the land" - this was the Lowland Clearances, earlier and on a much larger scale than the Highland ones. There is a recent book about it by Tom Devine if you want to know more.