I have this new shinshintō tantō that picked up at the Tampa show last weekend. I think the nakago read 'Sashū Mikawa Tensaido'. The reading of the signature is based upon the previous owners notes. The tantō is also dated on the reverse side.
Please note I am a professional Japanese fine art and antiques dealer and have studied Japanese language myself. I often don't need help with these type of things but i can't find any information about this swordsmith. I will at some point down the line use this information to help sell the Tantō.