Really?! I search a site with liturgical texts, googled it in Greek and English, checked Menologion - nothing!
Then I've propably mistaken. Amazon
mentions that the new edition of Fr. Seraphim's book on Augustine contains a service to Him. I might have mistook that as an akathist. Too bad that my local library's edition doesn't contain it.
The service to St. Augustine in Fr. Seraphim's book has Vespers and Orthros (along with a canon to him) for Augustine's saint day (June 15 in the Orthodox Church) but it has no Akathist hymn.
A lot of Akathists have been written recently. Maybe you should write one. I did for my patron saint, St. John of Damascus. A Romanus the Melodist I am not, but I undertook it with love and humility.