Not sure if you have this-
Coleraine Chronicle, 10 May 1862: At Cairncoggy, near Dervock, on the 4th inst., the Rev. John Millar, of the Free Church of Scotland, aged 64 years.
(Chronicle started in 1844; births, marriages, deaths indexed 1844-1869).
Since he was a minister these may be other bits written about him the time he died.
Also- 18 Jan.1868: At Benvarden Presbyterian Church, on the 15th inst., by the Rev. John Ross,, Mr. William Tweed, to Margaret Anne, daughter of the late Rev. John Millar, both of Benvarden.
"A History of Concgregations" says "On 13 July 1828 Mr. John Millar was ordained by the Presbytery of Ayr as Tobertdoney's first settled minister." There was later a dispute involving a lawsuit and after losing the case, Mr. Millar removed to Benvarden.
It might be worth contacting the Presbyterian Historical Society in Belfast for any details they might have on Rev. Millar. There was a church magazine (not sure if it was printed as far back as 1862) and I have found lots of information in it on ministers and missionaries.