Does anyone make an aftermarket barrel for the Gepard?
My error, apologies.
Technically an aftermarket item for the barrel but probably not you originally were after but the only thing I could find.
Perfect scale Modellbau also offers a conversion for ITPSV90 which is the Marksman on Leopard 2 used in Finland. You may ask if Gerold is able/willing to sell the guns and velocity sensors on top as separate parts.