The patch notes say that the warden class skill books have been added. This means they RNG anywhere in the world.
There was a time when the skill books were set, like sky shards. When the game first came out you could use a map to find a specific skill book in a specific location. But sometime in 2015 they RNG'd it. The shelves that at one time contained a smith book can now draw any skill point book. And as you learn more, any given shelf has a lower chance to drop one you need.
But the warden books should drop from anywhere in the world.
Btw I just found out that (unlike those in other zones) Vvardenfell bookshelves will reset after porting/relogging. So your best bet is probably to camp at the Library in Vivec and just keep logging off and on.