I've found a german website that only sells antique nihonto that are worthy of preservation.
There is a sword (linked above) claimed to be made by a swordsmith called Kamino Nagatoshi who is said to have lived in the Hyuuga/Miyazaki prefecture, in the Bunmei era (1469-1487) in the Muromachi period. My problem is that I couldn't find any information about this smith in any of the avaiable online swordsmith indexes (in english). I've tried everything and I'm clueless. I don't know how or where I should continue my research. Do you know anything about him?