I found a few items. Use "1805 Hanover Expedition" as a google search to get the names of persons involved in expedition – then expand search from there – Good Luck Steve
Expedition to recapture Hanover, December 1805 to February 1806:
Vol 1, History of the King's German Legion by North Ludlow Beamish.
link
In vol 2, at the end you can locate the units involved.
link
This one looks promissing! Part 5 of
Atkinson, C. T (ed.). 'Gleanings from the Cathcart MSS, 1 : Marlborough's wars (general); 2 : Marlborough's campaigns of 1707-8; 3 : Marlborough's campaigns of 1709-1712; The Netherlands, 1794-5; 5 : The younger Pitt's last venture : the expedition to Hanover, 1805-6; 6 : the "conjoint" expedition to Copenhagen, 1807. 6 pts.' Journal of the Society for Army Historical Research, 29:117 (1951), 20-5; 29:118 (1951), 64-8; 29:119 (1951), 97-103; 29:120 (1951), 144-57; 30:121 (1952), 22-9; 30:122 (1952), 80-7. Publisher: Society for Army Historical Research. NOT on Google. :(
The Life of His Grace Arthur, Duke, Marquis, and Earl of Wellington
by Francis L. Clarke:
link
Memoirs and Correspondence of Viscount Castlereagh, Second Marquess of
by Robert Stewart Castlereagh, vol 6:
link