All walmart cards are indeed 100% only for USA transactions. It wont work overseas.
Netspend.com is the fastest way, that's what I use to buy seeds overseas. You can get your free card online and have it mailed to you or buy one at any nicer gas station or other shops. Its only like $4 fee or something like that. But, most importantly, it works overseas and you can put $500 on the card at a gas station any time.