Sketches of Civil War Garrisons, &c

During the civil war, sketches and drawings were, no doubt, made of the lines drawn about divers garrisons. Some few of these have from time to time appeared as woodcuts: but I have a suspicion that several remain only in MS. still. If any of your readers can direct me to any collection of them in the British Museum or Oxford, they would shorten a search that has long been made in vain.