Squids, they are available from Nissan, part numbers:
* 56105-H5025 front shock absorber (for Datsun B110)
* 54320-N8200 strut insulator
* 40206-H7500 Rotor (not available from Nissan USA)

Or any Datsun 1200 strut cartridge insert should work. Which is to say there are only a few choices. They need to fit in 45mm struts. See Strut Insert Part Numbers. VW Golf inserts are a popular choice.

Why not just swap the struts over to large-brake B310? You'll get better brakes. Get the entire Strut/Brake assembly from Ralphs, only $45 each side + $18 for the spring. They will increase the front track 30mm (same as a stock A14-powered B310).

One of the best parts shops is rockauto.com. The rotors are getting hard to find. They are the 220mm rotors, only used by CAN A12-powered B310. But they were used outside North America for B210s, so are readily available. Best bet would be to find them within Canada, or mail order from another country.