You should be able to use any t-adapter. One end of it fits the t-ring, the other end fits into your scope's focuser. Just make sure you get the right diameter for your focuser.
As for the t-ring, one end is specific to your camera, the other end is generic. You will need one to suit the Nikon lens mount. Any reasonable camera store will have them or you can try ebay and other such places.
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