To my knowledge the HK clear mags are still the only option. Luckily the prices have come way down since the rifle's introduction. $48 seems to be the norm nowadays with a good amount in stock. Cross Creek Guns, HK specialist and Euro Optic has them at this price. Euro Optic does have a 10-rd mag listed at $25 alongside the same mag at $44 so I'm not sure if it's a typo so it may be worth trying.