To Amergin,
Blind Harry wrote "The Actes and Deidis of the Illustre and Vallyeant Campioun Schir William Wallace" in about 1477, first printed in 1508. He was also known as Henry the Minstrel and lived probably between 1440 and 1493. He probably gathered stories about Wallace and made them into verse form. He is known to have performed at the court of James IV. I don't think you could easily get hold of the text for the original, but a publisher in Edinburgh put out an edition of the 1722 translation/version done by William Hamilton of Gilbertfield, which was apparently the most commonly owned book in Scotland after the Bible in the 18th century. The title page of this says :
"A new edition of the life and heroick actions of the renoun'd Sir William Wallace, general and governour of Scotland. Wherein the old obsolete words are rendered more intelligible, and adapted to the understanding of such who have not leisure to study the meaning and import of such phrases without the help of a glossary" The new edition is called "Blind Harry's Wallace" and was published by Luath Press in 1998