I'd ten to agree with RealityCheck - don't bother with this and just apply to universities that don't require A level Chemistry, but study the content.
If you're set on taking A level Chemistry then be aware that the exam boards require any centre that enters you for exams also to offer you the practicals, which means very few centres will accept private candidate for Sciences. Before you commit to paying somewhere else to take the practicals, you need to be sure that there is a cast iron way of them counting towards your full A level - i.e. you are taking them at the same place as the exams or you have a written confirmation they can be combined.