If Bedieved one does not have Rashi Tefilin and only Rabenu Tam, is one allowed to say a bracha on Rabenu Tam?
ב"ה Shalom According to the Shulchan Aruch, one does not say a beracha on Rabenu Tam tefillin. ( Shulchan Aruch chaim 34:2). If one does not have Rashi Tefillin and by the time he will get them the time of Tefilla will pass, he should put on the Rabenu Tam tefillin without a Bracha. (Yalkut Yoseph) All the best