googling it appears that there is no factory window for this case.
To mod it yourself would be pretty simple, when you get the case have a look at it (there are quite a few air vent holes in the side) and decide where your window will go. cover the panel with lots of masking tape and draw out your window. drill some holes a couple of millimeters in from your line (the holes will need to be big enough for your jigsaw blade to fit in) then using a fine toothed jigsaw blade cut just inside your line. To finish you could use a sanding wheel on a dremel, otherwise a metal file to file back to the line and then fine sand paper to smooth it off.
You can buy rubber to go over the edge of your window if the cuts not that great, or you simply can't be bothered with cleaning up. but IMO it looks rather crap. a nice bare clean edge is best.
Next you need to decide if your going to use acrylic for the window or some kind of mesh (B&Q you can find both of these). With acrylic you then have another choice of fitting the acrylic inside or outside. I like outside, but you'll have to secure it wil bolts requiring you to drill the acrylic. Most people go for inside for ease - as you can just stick the acrylic to the inside of the case then.
As the forums rules state you we are not allowed to mention competitors, but there are a couple of companies out there that will do this job for you if you don't feel like tackling it yourself. However, it will cost!