Gabriel Munro's baptism is recorded in the parish of Farr registers dated 24th December 1804, son of Alexr Munro and Barbara Mackay in Armadale (shown below).There is no definite further trace of Gabriel except that he is surely one of the six males recorded as living in the house hold of Alex Munro on the 1811 census in Armadale. The parish of Farr census of 1811 only recorded the name of the head of house hold, number of males, number of females and how many people were employed in agriculture or trade. The census is available to view in the Highland Archive Centre, Inverness, Scotland.
It appears that Gabriel Munro was named after one of his father Alexander Munro's neighbours, Gabriel Reed, who is found on the 1811 Armadale census and who was one of the leading Sutherland sheep farmers whose Kilcalmkill farm stretched from Strathbora to the Strath of Kildonan. On the 1811 Armadale census Gabriel Reed had a house hold of 16 people including himself and 13 females. Garbriel Reed was raised in Northumberland, England where the Reeds were a well entrenched family, he had come to the Highlands in the mid 1790's. His first centre of operations was the Big-house Estate on the north coast of Sutherland which belonged to a gentry family, the Mackays of Big-house, one of whose members became his wife. Despite having put down these strong roots at Big-house which was on the boundary of the counties of Sutherland and Caithness, in 1813 Gabriel Reed agreed to take on the Kilcalmkill farm which had the attraction of what was reckoned to be a "good modern house" of a kind rare in Sutherland and which was no common farmhouse but a mansion-like plantation-surrounded home that belonged, until 1812, to Joseph Gordon. (Source: Set Adrift Upon the World - The Sutherland Clearances, by James Hunter, published in 2015 and which has extensive information on Gabriel Reed and his contributions to the Highland Clearances in Sutherland where the tenants were forced out to make way for more profitable sheep farming). (See also the 1811 Armadale census linked on the left).
As for Gabriel Munro a petition from his mother, Barbara Mackay, dated 18th August 1835, to the Duchess-Countess of Sutherland, as found in the Sutherland Estate Papers in the National Library of Scotland (REF:DEP.313.2420), states that two of her sons drowned in 1819 and two of her other sons had died more recently; one in Thurso and one in Liverpool. The eldest son, James Munro (b.1796), only had two children with the last being born in 1819 and no further trace of James after that. So it seems more than likely that James was one of the two who drowned in 1819. The fifth son, Honyman Munro (b.1806), has already been traced to Liverpool so it is more than likely that he is the one who died there. That only leaves the second and fourth sons, George Munro (b.1799) and Gabriel Munro (b.1804), as the other two who died early. It seems obvious to allocate George as the second eldest as the other one of the two who drowned in 1819, leaving Gabriel as the one who died more recently (as of 1835) in Thurso. However, there is a George Munro on record who was valuing houses in the village of Armadale in 1830 - which happens to have been a job that was previously carried out by their father Alex Munro. So it could be the other way round with Gabriel having drowned in 1819 and George having died later in Thurso by 1835.