Because they don't sell many of them most clerks don't know what they are, if possible try to go to the older clerks because they tend to have worked there longer and have seen them before. I've been to post offices that said they don't sell them then gone back later the same day and got some!

Thank you osiris! We'll check another post office in a bigger city today when we go up that way

IRCs are still available. Smaller post offices are either missinformed or plain can't be bothered to check (the head offices often stop sending them to the smaller post offices if they aren't selling well, so when they stop getting them, they think they're no longer made). Ask them to order some in, or try a different/larger store. Good luck.

I'm in Indiana in the USA. We're going out of town today so I may try another post office in another town

That is strange :s! I've been to the post office today and I've bought some!

Where do you live? Because in some countries they don't sell them anymore

I went to the local post office to try and get some IRCs for our overseas SAE and were told that NOWHERE sold IRCs anymore and that they were obsolete?