Where can I buy a Guild wars game key online?

I was going to buy it from plaync but then I found out they only accept credit card, I have paypal.

I suggest trying to order a physical, boxed copy of the game from Amazon or another similar site. Just make sure that it's new (unopened), as the cd key is what your money is really buying. You might encounter a small shipping charge, but even then it's bound to be cheaper than paying the full price at PlayNC.

If you live in an area where this option is not available, maybe you could send a query to support. I mean, doesn't PayPal require some sort of credit/debit card anyway? Perhaps someone at NCSoft could instruct you how to navigate their system with what you have.

No, just a bank account.

If you only have Paypal then you can't buy through the online store (ANET have already stated they won't accept it).
I doubt amazon.com accept paypal, although they might take verified paypal.

Your best bet is buying a prepaid Visa credit card and ordering online that way