Faranak,
To pay the FSW processing fee from Iran, you have the following alternatives:
1. Get the Credit card details of someone you know.
2. Ask a friend or relative abroad to get you the money order as instructed by CIC and then send the original money order to you via courier mail.
3. I have heard some money exchange agencies ("Sarafi") would get you the money order for you, but they will charge an additional amount of about $150 for that which seems really unfair.
For more details please check:
www.applyabroad.org
There, you can find helpful advices.
Good luck,