Our system will ignore IPNs resent for transactions that we have already processed and logged, since there is typically no reason to do so whereas doing so would produce usually-undesirable results (inaccurate txn logs listing the same txn twice, reissuing new download links or new PIN/license codes to buyers, etc.).
Even if we accepted resent IPNs, resending the IPN would not add any info that was not already sent and logged the first time around. If PayPal doesn't have that data to begin with, they cannot pass it to us. If you did not enable the Shipping/Buyer's Address setting for the product when the buyer first purchased it, then no address would ever have been collected during checkout, and thus no country data which would have been part of those addresses.
The best we might suggest is extracting Buyer IPs from your logs, so you could run a geographical IP lookup against those, as public IPs are typically assigned in country-specific blocks.