You can get things from airlines many different ways. Most are not as forthcoming with a large amount of items anymore. I did most of my writing to airlines (only write to an airline ONCE because if they are like most companies, they keep track of who sends in letters/requests and the dates... so if you send multiple requests, they'll know it) several years ago. I received lots of items from airlines many of you say no longer send out items. United Airlines, for example, sent me a box with amenity kits, a Schabak model, safety cards, inflight magazine, postcards, catalog of United items, pen/pencil set, stationary, etc. Reeve Aleutian Airlines sent me a large envelope with all of their safety cards plus a book on their history and several brochures/booklets. I even received a good sized package from Uzbekistan Airways. I think that due to the ideas people receive from sites like this, airlines are taking in a much larger volume of requests and simply can't fill them all on a cost basis. It does cost money to mail heavy packages or boxes to collectors. It does cost money to give away safety cards, models, t-shirts, books, etc. It may not be very much on just one item, but say every person on airliners.net writes to the same airline requesting free things. The cost does add up and is significant. Some airlines refer safety card collectors straight to the printing companies now.
I had some success faxing to a few airlines. Not many collectors try that method and often the fax number reaches a different department than snail mail letters. E-mail seems to be the least effective method. On many airline websites, the e-mail address simply goes to the website manager or programmer who wouldn't be able to fill any requests for memorabilia even if they knew what you were requesting.
Customer service agents at ticket counters/offices and gates sometimes will get items for collectors but that is becoming rare. The last couple of times I have asked flight attendants on board my flight for a safety card, I have told "Here is one, but you did not get this from me" and was also reminded to never just take one off of an airplane as they are required safety equipment. As my flight textbooks say, they are required under airline operations to be available for every passenger. It is a crime to remove them from an aircraft without permission. Airlines in the past have been heavily fined when an FAA inspector finds seats mid-flight without safety information cards.