BudsGunShop.com - 224 Valkyrie

The magazines Josh and Randy suggested will both work as will these.
budsgunshop.com/search.php?q=224+valkyrie&type=Magazines

No, you want ones for 224 Valkyrie, 6.8 spc. I'm in the middle of building a 224 Valkyrie now and plan on getting these mags, item number 2868041207CPD just type the item number into buds search and it'll pop up. Hope this helps.

no the 224 Valkyrie mags do not work reliably in the 223/5.56 mags here is a 28 round Valkyrie mag at3tactical.com/products/duramag-ar-15-stainless-steel-28-round-magazine-6-8-spc-224-valkyrie