Biver's

Bivers of Broadway are a specialist retailer selling clothing for domestic staff, and bespoke uniforms in your family's livery so that everyone can see you're affluent enough to (for e.g.) own a coach with two coachmen on the front and two beliveried retainers on the back. Presumably they don't trade in military uniforms or headwear, as this is the prerogative of Boult & Locke.