SSTV QSL Cards

Hello everybody,

I have a question. Recently I saw in ARISS' website that I can receive a QSL card as a confirmation of receiving an SSTV image during an event.

I am a licensed ham radio operator and I have a valid callsign as well as some QSL cards made by me. So my question is - how exactly, step by step should I send the ARISS my QSL card for receiving their SSTV image and how exactly should I receive their QSL card?

On their website I tead that I have to send them something called IRC, but I have no idea what that is and even if my country sells those(I live in Bulgaria). So if someone can help me, I'd really thankful!