The .375 Flanged is a great choice for your next double. Just be aware that won’t be your last as there is all ways a need for one more.
I talked to Nosler at the Dallas Safari Club show and they told me they would have their line of Safari ammo out this summer. I haven’t checked availability but it is another source for .375 flanged brass and loaded ammo and all their ammo is top notch.
http://www.nosler.com/Ammunition/Safari-Ammunition.aspx
Bill