If you have a sewing machine, you can design it yourself. The special style is more interesting. First, put a newspaper on the chair and make a stereo cut. Then, you should cut the cloth well. It shouldn't be too difficult
If available, you can buy it, but maybe the specifications are generic
If you have curtains, cloth, city and so on, you can go there and find someone to order it. You can give it to the size
