It is simply a metal ring at the very front of the lens which allows you to attach accessories such as filters, diopters, or in the case of modern video cameras - 35mm lens adapters.
Note the threads. Without them, you'd have to come up with some other way to make certain that whatever you put in front of the lens stays securely in place. Any variation in distance will alter focus, probably making a sharp image not possible.
Diopter is sort of a thrown around term for any wide angle, macro, or telephoto attachment that screws into the threads in front of a lens. x0.7 for example reduces the effective focal length by that multiple. So a 50mm lens with a x0.7 diopter functions as a sort of gimped 35mm lens. (roughly, someone should check my math since I'm just pulling that off the top of my head) It's not technically accurate to use that term for all of them, but it is easy. Search around ebay and you will see many of these items for various ring diameters.
I'm going to hazard a guess here and say that you probably won't find any lens accessories for that camera. It's not designed for a market that would purchase such things.
Mirror it? I'm not certain what you mean by that. What lens are you talking about at Best Buy? An actual lens, or a lens attachment (tele extender, diopter, etc).
If you are talking about an actual lens. No. Because a lens bends light rays to get them to converge to points on a plane at a precise distance from the rear element of the lens, you can't just put one lens in front of another and get a sharp image.
The only way to make that work is with a system like this:
There are an abundance of companies that make 35mm ground glass adapters. The problem you will have is that you don't have any threads to work with at the front of your camera. You
might be able to make it work with iris rods, locking everything down, then using some sort of DIY tube connector to ensure that the connection between the front of your camera and the ground glass box are light tight, set to a columnation (possibly the wrong word) distance that gives you sharp focus on the ground glass, and that all of that will stay locked down. You also need to be able to manually focus the camera itself and then lock focus at that point (along with zoom and exposure). Then you use the front lens to adjust aperture for exposure and to focus.
There are also DIY kits for that sort of setup, but it helps if you are crafty, have access to good tools, and know a little about optics and lenses - fortunately the latter is a minor requirement for building one of your own.
With a different camera that has a standard diameter ring with threads it would be a great deal easier, and you could probably finder diopter/extenders to work with.
What sort of image are you seeking to get out of all this? You mentioned a "problem" with your lens, a technical problem or a creative limitation?
