Are you appealing on the grounds of unsuitability or oversubcription, or both?
Even if the school is not supporting you, you should be able to obtain statistics from them on your child's performance at school, - Year end levels, Standardised scores, reading ages etc, which might help. These should be easy for the primary school to print off. You would need to enclose any evidence used in your initial appeal letter, but if it arises after then, you can send it off later, but obviously with enough time for the panel to look at it before the appeal.
When is your appeal being heard?
All the best