Buffalo has Bertram brass with proper headstamps here =>   (You need to Login

And 'formed from .303 here =>   (You need to Login

Unfortunately, both out of stock. I bought some of the Bertram brass and have formed from .303 as well to feed my 5 (really? sheesh) Dutch rifles. The forming is not too tedious but be sure to anneal the necks or they will split in one or two firings. FWIW, I annealed the Bertrams as well as they sometimes have a spotted reputation.

Holler back if you need any help. I would be happy to assist and I am sure others would as well.