Unfortunately nothing I read outright in a warrant or regulation. Comes from working on biographies of general officers and trying to discover why they diappeared from/were replaced in command. The army estimates in the Parliamentary papers would give the set establishments for each grade paid for by the army, home and abroad.
The closest that I can recall is the correspondence between Henry Torrens, Military Secretary to the Duke of York and Wellington on the June 1813 general brevet. Torrens sent blank recall notices to Wellington, for him to fill in the names of any newly promoted generals for whom Wellingon did not wish to retain or place on the staff of his army. The correspondence is in either Wellington's Dispatches or more likely in Supplementary Despatches.