Chrissy -

The best way is to use his Dispatches. At the beginning of each letter he lists the town it is written from. There are four different sets, all are Google Books. There are probably 40 - 50 Volumes total.

――.The Dispatches of Field Marshal the Duke of Wellington, During his Various Campaigns in India Denmark, Portugal, Spain, the Low Countries, and France, from 1799 to 1818. Edited by Lt.-Col. John Gurwood. London: John Murray; 1834-9.

――. Despatches, Correspondence, and Memoranda of Field Marshal Arthur, Duke of Wellington, K. G.
Edited by his son, the Duke of Wellington. ‘in continuation of the former series’ London: J. Murray 1857-80.

――. Dispatches of Field Marshal the Duke of Wellington, During his Various Campaigns in India Denmark, Portugal, Spain, the Low Countries, and France. Edited by Lt.-Col. John Gurwood. London: Parker, Furnivall and Parker, 1844-1847.

――. Supplementary Dispatches, Correspondence, and Memoranda of Field Marshal Arthur Duke of Wellington, K.G. Edited by the 2nd Duke of Wellington. London: John Murray; 1860-1871.

Bob