You do realize that not all oscilloscopes are the same size, right? Rigol makes cases for some of their instruments. None are listed as being for the MSO5000, but digging further, none appear to be for instruments that have dimensions particularly close to those of the MSO5000. That's why I asked.
The bag you linked to is for a DS1000, which has dimensions 325mm x 159mm x133mm (DS1000B) or 303mm x 154mm x 133mm (DS1000E).
The MSO5000 dimensions are 367mm x 200mm x 130mm, so essentially the same depth but significantly wider and taller than a DS1000.