You’d be surprised at how difficult finding a simple card case can be. Of course, I say that and then do a search and I find these other ones (below) that are in line with similar colors in a matte finish as well (though a little more expensive).
Available from Kikkerland Shop, 6.00.
Slender business card cases in anodized aluminum with matte finish. Choose from Black, Blue, Green, Gold, Silver, or Pink. $14.00 each. Available from japanesemoderndesign.com