Having listened to Andy M. Stewart sing it, the verse gives a list of weapons, musket, rapier, etc. In that context I would think the word is DIRK. No Scot would ever pronounce DARK, as DURK. One of the hazards of taking words from the internet - they are invariably wrong, especially where the lyrics are in Scots.

Internet lyrics are a great thing, but I always refer back to the original singer, and edit them as the mistakes show themselves.