The last 5mm Remington ammunition I saw was very pricey.I haven't seen any in ages.Awhile back there was company making a conversion for the 5mm. They sold the brass,dies and bullets. These cases used a primer.It was expensive for the conversion kit and the components weren't cheap either.I read about it on this forum but it's been along time ago.I think if I'm not mistaken it was on the Reloading forum.You might post in that forum. It might reapear if asked there.I can't remember the name of the company...........Good luck in your search.
Ruger Redhawk