In a previous life as a jobbing jeweller we used nickel silver wire and plate for making display rings and boxes. I'm pretty sure it came from the same wholesale supplier that provided our precious metals,tools and various other bits and bobs .
Failing that try looking-up non-ferrous metal suppliers . There is one called "Smiths" based in Horsham Sussex. It could be a long shot but might give you some ideas . Best of luck.