tribunal assistance for appeal against dla decision

Hi. Looking for suggestions on where we can find advice and support. Our son (3 years old) has been denied the mobility element of the dla, the decision maker clearly didn't understand asd and refused as they said there was an element of choice in whether he walks our not. This is not the case, anyone who saw him when he doesn't walk would see this. His difficulties when out are severely affecting where we can go as a family. I only take him on for places where I know I can carry him screaming kicking and hitting...i.e. Not very far. Our next step is to appeal the decision. What I would really like is someone to support/represent us in the tribunal. The organisation that have helped us so far used to do this but not any more. Can anyone point me in the direction of another organisation that can do this?

Thanks in advance