Food and litter: Carrefour, Megamart and any other supermarket
Toys, scratching posts, specialist foods (Royal Canin) and Misc: Al-Timimi Vets (Katara) and Parkview Pet Ceter
All within easy reach of WestBay - Good luck
Alternatively: Cats in Qatar are a willing source of advice

http://www.catsinqatar.com/CIQ/Home.html