Andy’s agent for cartoon work is Gordon Wise at Curtis Brown. You can contact Gordon via this page.
His agent for scriptwriting is Lily Williams at Curtis Brown. You can contact her via this page.
Andy also has a publicly available email where you can contact him directly. But before you do, please look at this FAQ post to see if your question is covered there. If it’s not, please get in touch using firstname.lastname@example.org – and a link to that is here.