You can get it fixed at any upholstery shops. Can find these shops in Musheirab/National Area on Al Asmakh Street. There is another one besides the Auto Decoration Shops on B-Ring Road in Fareej Ghanim Area near Crazy Signals.
However, if you want to change it...go to Industrial Area. There are quite a number of Junkyards/Scraps where you may find one. For instance, I can recollect one on Street 10 at Al Manajer R/A... and one in Street 23.