Go on the seed seller's site, they'll let you know thier particular procedure everyone is a little different.
You can find seed banks which take credit cards .
All you have to do then is get a gift card from VISA, MASTER CARD ect.
Some take international money orders ,some require cash .
TBG has a sticky at the top of "SEED BANKS" which will send you to a list of reputable resources.
This is a subject that is always a topic of discussion on this site ,do a little bit of research then dive in ,best way to learn is to do
Good Luck