Well, we do wonder if your emailer is thinking about May/Summer carols. Siwsi George recorded Mae'r Ddaear yn Glasu which might have been doing the rounds in the '80s but it isn't purely instrumental. There was a small volume of summer carols - a reprint of a 1944 collection, plus some additions - in 2017: "Canu Haf" (Summer Singing), Cwmni Cyhoeddi Gwynn (Gwynn Publishing Company), ISMN 979-0-708091-26-4. They're songs but tunes are often used without words.

sian