As was alluded to, Lowland families didn't wear Highland Dress and thus didn't have tartans- until the Allen Brothers invented a number of tartans for Lowland family names and presented them in their 1842 book
Vestiarium Scoticum.
Though experts raised their eyebrows at the time, these tartans have been in production ever since and have proven to be good sellers.
Another marketing tool is attempting to link every Scottish surname to a Clan tartan, which resulted in those lists referred to above.
These lists go back quite a while! My
1909 Leckie Graham catalogue has one. It does indeed give
MacCormack: Buchanan
MacCormick: MacLaine of Lochbuie
With full knowledge of the questionable authenticity of such lists, nevertheless were I in your shoes I'd probably go with one of these.
Some Buchanan tartans strike me as being garish, not my cup of tea. If I were a Buchanan I'd probably go with the Buchanan at left below. I've seen kilts in this tartan in person and it's beautiful.
Or if you want to go with a non-Clan "fashion tartan" the one on the right is called "Copper Haze" and was obviously inspired by Buchanan.
There's also a nice Buchanan with blue tones

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