Why not try your local flying clubs? You have a much bigger chance of finding some voluntary work there than at the airports. It would cost an airport so much money and it would take so long to process. Either get you security cleared and get you a pass, or give you a temporary pass meaning a member of staff would have to escort you everywhere. Its just not too realistic.
Like I said, flying club.
I have done at mine in the past. Anything from scrubbing planes down to preparing gift vouchers for trial/ pleasure flights.