Hi watslifeabout,
Sorry but I failed to locate any supplier for this, than going straight to their wesbites. They have their authorized distributors and retailers -
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We have a network of prepaid card point of sales across South East Asia and in some other parts of the world and we look forward to expanding our outreach worldwide. Electronic version is also available through some of our distribution partners, whereby you can make purchase and receive prepaid card number and password electronically upon successful transaction. To view the list of Garena Prepaid Card distributors, please visit Link hidden: Login to view and scroll to the bottom of the webpage. You can also get our prepaid card from the approved international retailers (Link hidden: Login to view).
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Hope this helps. :)