Another good option is the industrial kitchen supply store on Salwa Road. I wish I could remember the name of it, but it shouldn't be too difficult to find.

I'm 99% sure that it's either before or after the Decoration Roundabout on Salwa - on the same side as the Volvo dealership. I happened to stop in there once and was surprised at the decorating tips (icing) and other cake decorating supplies that they had.

Good luck!