Very few post offices in the US will know what to do with IRCs, particularly since they're not sold any more.

Since you have a US bank account, go ahead and print the click and ship label - but be aware you may *also* have to print out and fill out a customs form for the sender. Not having a date is fine. Granted, I do things domestically, but I've printed out a click and ship label where I've said the package will be mailed in a week (the furthest date available) and it's been longer than that before it's mailed to me.

I'm sure you know this, too, but don't send anything you don't want to not get back.

I'm trying to request an autograph of Ms. Emma Stone from South Korea on a 30"x20" <La La Land> poster, mailing it in a tube-shaped paper container to Culver City management address that this site provides. I'm looking into using 2 containers that smaller one being a SASE.

for returning postage, I calculated roughly $23 from USPS website, and I'm wondering how should I pay for that for self-stamping. I recognize a Click N ship option that I can print out a prepaid label, but as I cannot specify shipping date, I don't know how that would work.

having a bank account in the US, I can write a check for $23 and enclose it.

or I can buy bunch of international reply coupons, but I don't know if that works either.