It really wouldn't be right to exclude a good '45 "living history" group like Sir William's from the reenactor venue. Most such groups are quite serious in terms of authenticity, and hardly "RennFaire-ish."
They may not be "uniformed" per-se, but their historic counterparts were indeed organized into structured clan regiments (with a complete chain of command from the Colonel on down), or regional formations such as the Atholl Brigade. Far from being disorganized mobs, clan regiments of the '45 attained a fair degree of training and discipline....