https://www.midwayusa.com/reloading-brass/br?Cartridge=6mm%20GT&cid=670
https://www.midwayusa.com/reloading-dies/br?Cartridge=6mm%20GT&cid=702
All major die maker produce 6 GT reloading dies. As for brass Alpha , Lapua and Peterson are the ones you’ll find.
If you’re looking for .348 bullets Fury has some.
https://www.furycustombullets.com/shop-2/35-caliber/348-220-grain-flat-point-bonded-50-pack/
Then there is Cutting Edge and Hammer but those come at a premium price.
UPS and Fedex are both horrible here. They both show out for delivery and it shows up a day or two later. UPS was here the other with a couple of packages , but no powder. I think they have a habit loading packages on the wrong trucks.
My powder did show up today and it is an extruded powder so...
I’ve had several problems with them dropping the ball. They include 2 different bullet orders that never shipped and an order of brass that was wrong. On this powder order UPS is the problem child for me. Tracking showed it out for delivery yesterday , still waiting. Hopefully tomorrow.