
Been using
google books lately to further my research, there is a vast library available through google books unfortunately at present many of the books can only be viewed in snippet form for legal reasons because of copyright. Google are currently trying to come to an agreement with publishers regarding this so hopefully one day all content will be freely searchable.
Below are 2 of the earliest references I have so far been able to find for the name McCorkell:
Criminal trials and other proceedings before the High Court of Justiciary in Scotland
By Robert Pitcairn
Page 352 Year 1550
Jun. 28 — Donald McKv Of Far, Neill Mcane Moir, Rory Mcane Moir, Murdoch Mcane More, John Mcane More, and Tormat Mcane More, brothers, and Donald Dow Mccorkill, charged for the cruel Slaughter of Alexander M"ane Rois, Alexander Mcillemychell, Tormat Makalexander, and five others. Alexander Rofs of Balnagowne was amerciated for not reporting and delivering to the Clerk of Jufticiary, the Letters, which had been purchafed by the wives, children, parents, and friends* of the deceafed, duly executed and indorfed.
Ah well every family throws up the odd bad egg!
A history of the Highlands and of the Highland clans, Volume 1
By James Browne 1838
Page 274 Year 1614
When Sir Robert Gordon heard of these occurrences in the north, he returned home from Edinburgh, where he had been for some time ; and, on his return, he visited the Marquis of Huntly at Strathbogie, who advised him to be on his guard, as he had received notice from the earl of Caithness that Sir Donald meant to create some disturbances in Sutherland. The object the carl had in view, in acquainting the Marquis of Mackay's intentions, was to screen himself from any imputation of being concerned in Mackay's plans, although he favoured them in secret. As soon as Sir Robert Gordon was informed of Mackay's intentions, he hastened to Sutherland; but, before his arrival there, Sir Donald had entered Strathully with a body of men, in quest of Alexander Gun, the burner, against whom he had obtained letters of caption. He expected that if he could find Gun in Strathully, where the clan of that name chiefly dwelt, they, and particularly John Gun, would protect Alexander, and that in consequence he would ensnare John Gun and his tribe, and bring them within the reach of the law, for having resisted the king's authority; but Mackay was disappointed in his expectations, for Alexander Gun escaped, and none of the Clan-Gun made the least movement, not knowing how Sir Robert Gordon stood affected towards Alexander Gun. In entering Strathully, without acquainting his uncles of his intention, Sir Donald had acted improperly, and contrary to his duty, as the vassal of the house of Sutherland: but, not satisfied with this trespass, he went to Badinloch, and there apprehended William M'Corkill,one of the Clan-Gun, and carried him along with him towards Strathnaver, on the ground that he had favoured the escape of Alexander Gun ; but M'Corkill escaped, while his keepers were asleep, and went to Dunrobin, where he met Sir Alexander Gordon, to whom he related the circumstance.
I particularly like the second snippet, it puts McCorkell firmly in the clan Gunn, although I have always heard the name McCorkell was a sept of Gunn this is the only direct reference I have seen to an individual in the clan.