Although this may look like a chemist from the front, I urge you to go inside as these shops have a great range of gluten free flours. They stock most of Bobs Red Mill Flours and also a range of gluten free crackers, cereal and pasta.
There are branches in Bridgetown, Christchurch, the Sheraton Mall, Speightstown, West Coast Mall in St James .
The range of Gluten Free products, apart from the flour, may vary from branch to branch, so if there is something specific you are looking for, you may want to call ahead. All contact details for each branch are on their website.