If you want stock replacements, there is a Nissan Dealer in North Carolina that has the last oem 200SX strut insert. Rock Auto has one aftermarket strut in stock too, so if you could track down both, you would have a complete set although different brands. Datsun 510's used them as factory replacements for the old style rebuildable cartridge (the dealer would gut the rebuildable innards and drop in the 200SX insert) and 810's also used them. But I have no luck searching for 810 or 510 strut inserts.
The best thing to do is get 280ZX inserts, and use about a 1" spacer (I used washers) to keep the insert snug inside the cartridge.
I paired mine with cut 510 springs to compensate for the shorter stroke of the ZX inserts, and the ride is great.
Or you could be really awesome and get coilovers for the 510 and bolt them up (they are rumored to fit.)
Here's how mine looks with the hybrid setup.
Just to let you know, the most difficult part involves detaching the brake lines from the strut.