I have delt with this exact thing several times and I can tell you from my experience that you are out of luck with the Paypal dispute.
You see, Paypal will ONLY find in your favor if the tracking information shows DELIVERED. If it says anything else, like ACCEPTED or IN CUSTOMS, they will not find in your favor and the buyer will get a refund.
First Class Internationl is NOT trackable at all. When you ship an item out that way, you are bsically sending it without any insurance, no tracking, and no idea when and if their package even makes it to them. If you ship Global Priority Mail Flat Rate Envelope, it is also NOT trackable and you cannot file a claim with it at the post office. If you send regular Global Priority Mail then you are supposed to get detailed tracking information, but with my experience it is also not fully reliable. The only form of shipping that is reliable is GLobal Express. Although expensive, it is worth it. You get $100 in insurance and it will be fully trackable and will make it to the destination quickly.
What you can tell the buyer is that they paid for First Class International and to please give the package 60 days to arrive. Also, advise them that the package may also being held in their local customs office and should check there to see if it is being held for any custom fees. Did you put a receipt in the package? Did you mark it as a gift? If there is no receipt in the package, it will delay it. Also, if it is marked as a gift and it is an Ebay purchase, your package will get lost., I guarentee it. I used to have tons of packages lost out there when I marked packages as a gift. As soon as I started putting receipts in the package as posting the real Ebay value the packages stopped dissapearing.
ANyway, good luck!