Just email them and ask them in a polite manner for what type of things you collect.
A couple of airlines which are very generous include:
the British charter airlines
For starters, just stick with the European airlines as they seem to be the best, even airlines like Cyprus Airways, Olympic Airways and Corsair send stuff out.
If you need some link take a gander at my links site
It has links to airlines' websites and also has email addresses where known.