In the event that you experience this kind of issue in the future, if you have not included international postage on your listing then before you reply to the buyer stating that you would be prepared to post the item to his/her country go back and revise the listing, making sure that you add an overseas postage option. Whilst you are doing this make sure that the destination country has not been set as a country that you do not post to. If it has, then deactivate the block and save the latest updates to the listing.
Once you have done that reply to the buyer's message, stating that you are willing to post the item to his/her country of residence and that you have also added an international postage option to the listing. That way if the buyer is willing to pay the price for the item, including the overseas postage costs, all he/she would need to do from that point onwards would be to go through the Checkout process in the normal manner and once you have received payment for the item you can then post it out to the buyer.
