I'm not sure when Nerf plans on releasing their version, but I finally completed the second revision of my Nerf Rival drum magazine. Will be testing this once all the hardware comes
Nerf Rival 12-Round Magazine Refill Pack - Entertainment Earth
Amazon.com: NERF Rival 12-Round Magazine : Toys & Games
Nerf Rival 7-Round Ball Magazine – Blaster Barn
Nerf Rival 18-Round Refill and 12-Round Magazine - Walmart.com