If you really want white vinyl, I doubt any maker produces a universal corner that will fit any angle. Nor would they produce just the precise angle you need - there's not a market for one-of-a-kind angle pieces.
Depending on the makeup (size, shape, style) of the vinyl pieces, maybe you could make your own wood angle pieces and paint them to match the vinyl. If you do that, I suggest cedar.
Another option is to not use corner pieces at all. Simply "stop" the fence at the corner from both directions, with the two "ends" touching.