AmazonUS (via first2sav) has already Fujifilm X-T3 half cases for sale. The popular Kaza leather half cases will be soon available for X-T3, too.
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Fujifilm X-T3
USA: BHphoto, AmazonUS, Adorama, Focuscamera
AUS: CameraPro
EU: CalumentDE, DigitechCH, WexUK, PCHstore, AmazonDE, AmazonUK, AmazonFR, AmazonIT