We had an HR Coordinator for compliance purposes while we had most of our HR work outsourced to a well known functions consulting firm. In Oct 2012, our company was acquired by a larger firm and in Jan 2013, I had completely transitioned out of it. So right now, I am not associated with that company even though I founded it, the HR Coordinator that I had has moved on to other places too, while the new administration of the company does not know me as an employee.
I have a lot of correspondence, legal documents (such as old incorporation certificate, tax forms and statements, valuation and acquisition documentation etc.) but I do not have a letterheaded certificate from someone else saying that I am/was the director of that company. I had thought of self-certifying in form of a statutory statement/affidavit and attaching with it the documentation mentioned above. Still not sure if that will suffice.