Any reason why it must be "spring" wire?
There at 2 options I can think of. 1 is mig welding wire comes in 0,45mm, 6mm, 9mm and 1,2mm. Check with welding suppliers.
Option 2 is to contact a spring manufacturer, they can straighten and cut for you.
If you still can't come right, let me know and I'll get it for you.