Never use walmart for a visa gift card or a money card. First of all, they charge you for everything with those cards. Second they investigate all transactions to make sure you are "supporting terrorist activity" and i'm sure buying cannabis seeds will fall under that category these days. Instead go to walgreens and buy a visa gift card there, but make sure it doesn't say "visa vanilla" because visa vanillas can only be used in the United States.
topo, you could try world wide seeds, they are a bit cheaper than attitude so you could still get 3/4 quality beans with your 50 bucks. As far as the card and security goes, i'd go ahead and try it, I don't think they would try to arrest you if it didnt work. I think the worst that could happen is a denial, oh and good luck hidding this from your wife lol!