I would like to book the greek island passes for 4 days in 1 month for 2x youth and 2x adults. Our trip starts on August 15th. About this I have the following questions:
My experience it´s not possible to get this pass as mobile version 
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20th August is the earliest because Eurail needs time to ship the pass to you :)
Maybe a ticket office or travelagency next to you sell the Greek Island Pass For example NS International Ticket desks or Treinreiswinkel worths a try :)
Seewulf is right. The Greek Island Pass is only available as paper Pass. You can also let it be shipped to your accommodation in Greece if the delivery time and the length of stay in Greece allow for it.
As we sell our Passes online, we do not have the information on where these Passes might be sold. From other customers their experience I know that, at least in Greece, the Pass was not being sold at the train station in Athens and by Blue Star Ferries. You could try to contact the Greek railway carrier '’Trainose'’, perhaps. I hope this helps. Cheers,
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