I've lost mine too. I contacted Fuji and was staggered by this reply:
Thank you for contacting FUJIFILM UK.
We are sorry to hear you have lost the eye cup and to advise, this part is not available separately and is only included with a replacement viewfinder. The camera will require workshop attention, please reply with your UK address details and the serial number of the camera. We will send you prepaid packaging which you can use to return the camera to our service department via Royal Mail special delivery.
Alternatively, please visit the following link to prebook your camera for a eye cup replacement. Please do not include the any lens, battery, memory card, any leads or the charger with the camera. We sincerely apologise for this inconvenience.
The Fujifilm X World Team
I have to return the camera for a push on part costing pennies
Edited by jhjl, 13 May 2016 - 10:33 AM.