You know should be able to get them new still for around $60.
Also you know that the most Datsun's from the 70's through to 1986 all share the same spline count/size so you don't have to ask for a 240z one.
So I know the following also work
Datsun 1600, 180B, 200B, early Skylines/240K upto 86, 720 Utes, 160J + Stanza, 280zx
So sometimes you have to ask for one of these as those guys that work at places that sell wheels don't know jack from jack as the manuals/catalogues don't say.