I would try the same places at tomica, but I think Narita and Haneda airports both have stores that have a lot of die cast airplanes. In Narita, in Terminal 1, its like on the 3rd floor close to the observatories. Haneda, it was like 3rd floor too, close to the observatory deck.

Also you might try Tokyu Hands http://www.tokyu-hands.co.jp/foreign.html