Ebay.
http://www.ebay.com/itm/SET-SIX-Brand-New-Fuel-Injectors-1981-1982-1983-Nissan-280ZX-2-8L-TURBO-/190667834032?pt=Motors_Car_Truck_Parts_Accessories&vxp=mtr&hash=item2c64b042b0#ht_1550wt_907
I've gotten em a lot cheaper than that, but thats the cheapest set I see on ebay atm which is pretty much the same price as if you were to get the injectors that autozone has to offer.
http://www.autozone.com/autozone/parts/Gp-Sorensen-Fuel-Injector/1983-Nissan-Datsun-280ZX/_/N-ikmwtZ8vd08?itemIdentifier=79703_2390_6207_