Cover on dash replacement

Replace it as in put it back on or replace it as in it is broken and I need a new one? If it is the first one it should have clips that snap into place. If you could take a picture of the opening and the part I can confirm that.
If you mean you need a new one, that would likely be a salvage yard only part. Trim parts are not a really common aftermarket item unless it is a very popular vehicle.
If you are in the US you can try http://www.car-part.com/. Enter in your vehicle information and select a part like a fender or door. They list member parts yards and normally will have pictures that would let you see if the interior is the same color. Then you can call the listed yard and see about the cover.