Housing

If you are purely for beauty, then here either take sheet metal yourself and cut out everything you need from it, and then paint it with some kind of spray can, or search on sites like Avito who does this. What would someone else sell a non-glass side cover separately, you are unlikely to find.

But if you thought of this in order to improve cooling, then I will tell you one thing, that you do not need any large fan on the side wall. There must be good through air circulation in the body - from two adjacent sides the air must be taken in from the outside, from two opposite sides it must be blown out. Or climb from one of them, and blow out from the opposite. Well, in general, blow through the case so that the air heated by the internal components of the system does not stagnate inside. This will be enough to keep the components from overheating. On the extreme, if you need to blow off the VRM zone of the motherboard, instead of a tower cooler, you can put a box-type cooler on the processor, but a more efficient one, for example, SCYTHE Shuriken (I wrote the model just offhand, it is more expensive, it is cheaper). You can also put a fan on the top cover above the VRM, which will blow air out of the housing upward, outward, if the housing has such a function. And the fans on the sidewalls (no matter how big or small) simply break the airflow, interfering with normal circulation, at best not bringing any benefit, and at worst reducing the PC's cooling efficiency.