2nd choice 270 WSM brass

I don't have any experience with 270 wsm. When I've bought new brass I've had good luck with Hornady for my 35 rem. I load +p loads for it. I've also bought Winchester brass for my 357 mag. Of course neither are anywhere near the pressures of 270 wsm. If it were me I'd try Winchester.

Lapua and Peterson come to mind

From my experience, you won't have many choices. When my son was looking for some for his Norma was the only thing he could find.

Certainly, recycling some factory ammunition to get the brass is an option. I will warn you the stay away from anything Federal. We bought some when he got his rifle, and the primer pockets were loose after the first firing. They load that stuff pretty hot.

In a perfect world I'd get Winchester if it was available.

ETA: I just checked on Midway and they show 3 options, Hornady, Nosler, and Remington. Hornady has good reviews.

For reference I have a 300WSM and have been collecting brass for a while. With mine the plated WIN brass is the longest lasting I have used so far.