Calskit

Recently got a Nemesis x9 and have been looking for a drum mag that fits the RIF. Apparently the c&g drums that are used with the ARP-9 don’t work with the X9, but the X9 fitted mags work with the ARP-9.. weird. I’ve been looking at the Classic Army Electric Drum Mag that seems to come with the PX9 in a bundle package, you can also purchase it separately but I’m struggling to find it anywhere in the UK. Does anyone know where I can find one? Or suggest a drum that fits the X9? Cheers!