Is 3157NA interchangeable with a regular 3157? I want to swap the corner and parking bulbs to chrome or red but I can't find a 3157NA in anything except amber (I don't want LEDs).
You can't find it because NA stands for Natural Amber.
You can get a plain old 3157 which has no added color, designed for use behind a colored lens. You will not find a red colored 3157, except for possibly at a ricer shop. There's a good reason for that.