There is apparently, at present, not a single public Mass according to the preconciliar Roman Missal in Croatia, either in Latin or in Slavonic (the "Slav-Latin" or "Glagolitic Rite" in use in parts of the former Yugoslavia -- including in Croatia -- from time immemorial until the 1960's), and it's not due to lack of interest among the laity. Since 2008, various lay faithful of Zagreb, Croatia have been pressing for the application of Summorum Pontificum in their archdiocese, apparently to no avail. The complete correspondence of the Traditionalists of Zagreb with the archdiocesan officials and with the PCED can be found here (with English translations). The October 28, 2009 letter from the Archdiocese of Zagreb denying the request for a TLM of thirty faithful from 20 parishes is a particularly instructive example of the art of using the text of Summorum Pontificum in order to obscure its obvious meaning and to frustrate its implementation.
Today, the Croatian blog Toma Blizanac has published the following letter from the PCED:
Pontificia Comissio "Ecclesia Dei"
Vatican City, 25 November 2010
Dear Mr. ---,
This Pontifical Commission would like to thank you for your kind letter of 8 November 2010.
This Pontifical Commission is able to inform you that after contacting His Eminence Josip Cardinal Bozanić, it has received the assurance of His Eminence that the Holy Mass in the Extraordinary Form will be celebrated in one of the churches in Zagreb.
With every good wish, I remain
Sincerely yours in Christ,
Rev. Mons. Guido Pozzo
Thanks to Marcus M. for the tip.