Remathilis
Legend
Which has been my point in classes all along.Paladins aren't really a problem for Dark Sun - now they are not required to be lawful good and wear full plate. They can just be refluffed to Templars. You could do all the PHB classes simply by replacing subclasses.
It's the races that need to be different to make a setting feel different.
As for races, there is a variety of options. You can use current races with some changes (such a wood elves representing Silvanesti), you can add world-specific subraces (such as an Athasian elf subrace or a kender subrace for halfling.) You can rename and refluff races (dragonborn as dray, half-orcs as calibans) our you can replace them with a race that fills a similar niche (half-orcs don't exist, but minotaurs fill the brute role).
Further, we only need worry about finding places and replaces for the 9 phb races; supplement races are supplemental. If they fit (such as genasi in DS) but there is no onus to fit everything in every supplement.