I got my 30 Newton headstamped brass from Quality Cartridge. Kind of pricy (three bucks apiece)but decent looking brass.
It's my intent to build a rifle in each of the more common Newton calibers (the 256, the 30, and the 35).
What I really want to see is Remington introducing the classic 700 chambered for the newton cartridges. This might get us affordable brass as well as some modern rifles.
For my Newtons I'll be using a pre-war model 70 (30 Newton) a model 54 (256), and a model 30 Express (35). All actions for which the Newtons would be appropriate and models which should have been produced in these chamberings when they were made. GD