The orderly book sometimes called "A British Orderly Book" and sometime "Cornwallis Orderly Book" is difficult to find because it is actually the Major General Alexander Leslie Orderly Book. It covers the time period 28 August 1780 to 20 March 1781.
The Leslie Orderly Book was transcribed and published by Professor A. R. Newcome and appeared in all 4 articles of the North Carolina Historical Review during 1932. It has been called the “Cornwallis Order Book”, but it is better described as Leslie’s orderly book which also copied Cornwallis’s orderly book after the two commanders joined forces on 18 January 1781. Making such copies was the common way to disseminate the commanding officer’s orders to subordinate units. Note that Cornwallis’s “General orders” are followed by Leslie’s “Brigade orders”. The copying task was the responsibility of the brigade and regimental adjutants. The record of these typically daily orders was called an "orderly book". So this document is Leslie's record of all orders he recieved from his superiors, notably Cornwallis, plus any he added and passed on to his subordinate regimental commanders. After dissemination down the chain-of-command, all orders were read to the troops.
Here is the entire document in PDF format.
This source is available online in these four articles:
Use the page numbers to efficiency scroll to these articles.
This source has a wealth of information about the daily operation of these military units. It includes details about the British units and their order of battle during the Battle of Cowan’s Ford. This source is essential to study Leslie’s movements during August 1780 to January 1781.