Model/Config.php
public function getGeoIpMappingForCountry($countryCode)
    {
        if ($mapping = $this->_scopeConfig->getValue(self::XML_FASTLY_GEOIP_COUNTRY_MAPPING)) {
            return $this->extractMapping($mapping, $countryCode);
        }
        return null;
    }
public function getGeoIpMappingForCountry($countryCode)
    {
        if ($mapping = $this->_scopeConfig->getValue(self::XML_FASTLY_GEOIP_COUNTRY_MAPPING)) {
            return $this->extractMapping($mapping, $countryCode);
        }
        return null;
    }
Get store ID for country.

@param $countryCode 2-digit country code
@return int|null