score:2
Thanks to the author, Glenn Farris, I obtained a copy of "Report on a Project to seek out documents describing early 19th Century California housed in the Russian Naval Archives in St. Petersburg, Russia". It contains a translation of a 2005 letter from the director of the Russian Naval Archive (RGAVMF), Vladimir Semenovich Sobolev, who describes the archive's holdings: "There are original journals kept during the voyages of V.M. Golovnin and L.A. Hagemeister.". I believe that the latter is the document in question.