I have looked at thousands of these on ebay and the net. All the ones I have seen with a magnifying lens above 2x have either a special case that the lens attaches too or the lense is fixed to a bracket & stand. There don't seem to be any variations in cases for the 8x lens.
There are fisheye , macro and 2x telephoto lenses available that can be used via a magnetic ring that is stuck around the camera. You should be able to use these with a case of your choice as long as the area around the camera has enough room for the ring to sit properly. Im not 100% sure on this but what I have read so far seems to be the case.
There are a couple of high quality custom setups available where the case looks a bit nicer but they cost like $100 or more and will only suit a particular phone.
Currently using : Samsung S4 i9505 4.3 stock rooted.
Previous Phones : Samsung Galaxy S3 4G - Galaxy Express - HTC Incredible S - HTC HD2