From the OPs other posts they live in the USA, where you will not be able to buy an IRC.

it sepends on the country where you live. Some countries issue IRCs, some don't. If your country does issue IRCs, you can buy them from your post office, preferably central one, since small post offices might not know, what an IRC is. You then preferably get it stamped in the left field and enclose to the letter and pictures you send to a celebrity. Wait for a reply. That's it.

Celeb will use this IRC to exchange it for appropriate postage in his country and it will cover the costs of mailing you the signed photos back.

Where do you get one and how does it work? Help would be greatly appreciated