Viltrox recently announced a new DG-L macro extension set with 12mm and 24mm tube rings (price: $54) designed for Panasonic/Sigma/Leica L-mount camera systems and the first review is already available online:
The Viltrox DG-L macro extension tube ring set can be purchased directly at the Viltroc online store (they offer international shipping) or in the US from B&H Photo.
Additional information on the new Viltrox DG-L macro extension tube ring set for L-mount cameras: