I was recently introduced to the concept of a "Kaddish Yachid," attributed to Rav Amram Gaon. A few fairly unreliable sources online discuss it as some form of a stand-in for when Kaddish can't be said in a minyan (ex. 1, 2), and the person who originally introduced it to me only had its text and authorship.
However, when I try to search through the Seder of Rav Amram Gaon for this, I can't find any reference to this.
If this was actually written by Rav Amram Gaon, where can I find it in his writings? If not, who actually wrote it, and where?