I know the importance of having the part then and there when you need it rather than waiting weeks if not months in lead times from suppliers. Only removed due to service discolouration.
Perhaps you could get them recoated / painted? The item "GENUINE PORSCHE 991 GT3 TURBO RS 911 CENTRE LOCK WHEEL NUTS SET 997 99136108190" is in sale since Sunday, August 12, 2018. This item is in the category "Vehicle Parts & Accessories\Car Wheels, Tyres & Trims\Centre Caps". The seller is "freed_co" and is located in Penshurst. This item can be shipped worldwide.