I have a right side mirror. It isn't much use. AFAIK there are not ones available with convex glass nor is just the convex glass available. The good thing about the huge greenhouse on an E3 is that you have a pretty clear view of the right rear without moving your head much.
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Dick-- I have been driving for 60 years. All of my cars and SUV's that I used to tow a boat had flat glass left and right mirrors. Back in the 70's, I would take the convex glass out of the right mirror and replace it with flat glass so when I looked in either mirror,I was seeing all surrounding areas at the same distance.
The key was the mirror settings. Your left mirror should be set with your head up against the door glass and the mirror is set to see down the side of the car.
The right side mirror is set with your head in the middle of the car directly behind the interior rear view mirror. Then set the right mirror to see down the right side of the car. You will now have no blind spots and the outside mirrors will only see the road on both sides and your interior mirror will see out your rear windscreen.
All of this can be confirmed by parking your car next to another car that would be in your blind spot--left & then right. You will see the car in your mirror with just a slight head & eye movement.
Most people set their left mirror to see directly behind them,and then use their interior mirror to fix their hair or makeup. You know these drivers when you see their face in their outside mirror when you're directly behind them. They can't see you when you're beside them.
The flag mirrors on our E9 &E3 when set correctly will give you a full view of what's behind and beside you. The Trap. mirrors on my 1972 2002 showed less,but the traffic wasn't nearly as dense 50 years ago as it is today. Drew