Do you have any credit cards at all? Amazon.com will process most cards, as long as you give them a US address. Some don't work, most do, it seems to be somewhat random.
Just create a new user account as if you are American and give it a try.
You can get an address by registering on viabox.com for free, or just by googling a random address (hotels, businesses...).

P.S. I don't know about those survey sites, I'm very sceptical of their ulterior motives.

EDIT: If you have PayPal, you can shop at pcgamesupply.com, but they will charge you a few dollars commission.

what Burek said.

http://www.pcgamesupply.com/buygames/sony-playstation-network-cards/

You can pay with a credit card from any country and they give you a code from any country, instantly.

I used it to buy UK PSN cards, with a Japanese credit card.

Like Troll_Whisperer suggested.

I too use pcgamesupply.com. After the initial weird setup where they send a code to your phone number its all fine. The PSN code is generated within 30 minutes max.

Only thing is the prices arent the greatest.

I´ve heard good things about Play Asia.

I´m not 100% sure how it works though.

That will work as well, you can pay by PayPal and get your code in the mail. 

They also charge commission.

Due to time zone differences, sometimes you have to wait several hours.

I still suggest attempting to buy from Amazon.com first, and use others as a backup due to them being more expensive.

Really I could find one in my 7-11 lol.

I wouldn't bother with those surveys.

Those games are free on PSP. Well almost everything is free on PSP