Winchester quit making loaded ammo in the mid to late eighties about the time I bought my first Contender chambered in .256. Shortly after that or somewhere around that time they quit making brass for it. As mentioned, Quality Cartridge among others makes it.
I have seen mentioned (besides using the seating die) using a 30 Mauser die for an intermediate step. Fortunately I'm still running on brass from my first few boxes of ammo and the two boxes of virgin unprimed brass I found in a pawn shop back in the 90s. However I did toy with forming some from 357 cases just for grins. I did it in one step without annealing and losses were as high as 20% with brass cases and almost 100% loss when trying nickel plated.
I have an old RCBS catalog that lists forming dies, but they were prohibitively expensive. If I remember right, they were close to $200 back in the 90s. If I were you I'd just use the seater as mentioned by rescue_171 or try the 30 Mauser sizer for an intermediate step. Annealing may help, but since I was just playing around I did not try it.
Curtis