Are we talking about a reversing camera here?. If so, there are plenty of options for aftermarket ones, some wired in, some wireless. Just look it up on ebay or amazon. As you are unsure, i'd suggest amazon, then you can have the results graded by customer rating. Look for something which has been rated at least 4 out of 5, and preferably by at least 50 customers. As for their usefulness, i guess that depends on the car, your ability to judge where the back of it is, and how often you are likely to be parking in a tight spot. There is a reversing camera on our honda jazz, but to be honest, the only time i use it is when i go and visit my pal. He has a fairly short drive and it is usually difficult to find a space on the street. So with the camera i can back right up to his car with only a couple on inches between them and not be blocking the pavement. But remember, if the lense of the camera is dirty, they are useless!. Under most circumstances, i don't really see any point in getting a camera over parking sensors, certainly on a smallish car. Different for something really big, like a large van, bus or truck.

Sarah, your choice of working is a source of confusion!

I had a reversing camera on my former car, Nissan Primera, loved it, I could park up close to items like bollards and not hit them, presently I have reversing sensors on my present car and whilst it is useful, it is not nearly as good as actually seeing what is right behind using the camera.

As for dirt on the lens, I never suffered any problems, but am aware the problem does exist as Skoda fits a washer system to their cars.(well the Rapid when I looked at it last summer)