I was wrong about the images I've seen of King Charles in a simple jacket such as the one sought by user <pageone>.

I've inserted an image of him when he visited Lochcarron Mills in the fall of 2023. The jacket has 2 buttons, but bottom one is obviously decorative. Kinloch Anderson does offer jackets cut in the same fashion, but with only one button.



Separately, Dr. Miles Kerr-Peterson, from Gaelic Themes/St. Kilda Kilts, tells me that their "Wallace" jackets are cut with lapels that meet a bit higher on the chest, whether the jacket has 2 or 3 buttons, but that they also make a jacket with lapels shaped like those worn by HRM. They are less expensive than those sold by Kinloch Anderson.