Today I went to a second post office to try to get some international reply coupons but they were also out. I went to usps.gov to see if they are for sale online but they're not. But I learned that new IRCs are coming out on the first of September, and the new price is $1.85. I found this webpage which explains the issue nicely:

An international reply coupon primer: http://www.n6hb.org/s-a/irc.htm