TRY THIS TRICK :
At amazon.com, type "hard shells for 17" MacBook Air" in the search. you might get results like this:
https://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=hard+shell+for+17%22+MacBook+Air
Of course, you have to bear in mind that there is no 17" Air.....
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