I think I can be a big help to you with this, Marcus. I in fact just got done with a post-apoc setting using the WoD system.
The book you want to look for is in fact very new, entitled "Mirrors". The book is in fact a compendium of alternatre rule systems used for different types of story you might want to play. The Apocalypse settings invovle almost a dozen different ways the world as we know it can come to an end, from an act of god to economic collapse. The book covers things like CBRN and exposure, hunger and foraging for food and water. Its basically everything you need.
They give tidbits of information as to how that would impact each branch of WoD, but if you want to make a mortal player group, a couple of things you will have to watch out for that were pitfalls in my own game.
Survival in a post apocalyptic world is a matter of course, and its very easy for a group to settle into a rather not fun rut of scavenge-sell-scavenge-sell. Try to avoid this by instituting a more passive search system for scavenging. I recommend a single roll of Wits+Suvival/Investigation (Wilderness or Urban respectively) to represent them finding anything of use or value in a single location or storyline. It streamlines the process and you don't spend half of your game time with your players looking through garbage.
The post apocalyptic society can be a hard one for goals as well. I tried giving my own group more freedom in what they could become or what they wanted to accomplish and in retrospect, that was a big mistake. I would recommend giving them some kind of ultimate goal in mind. Possibly a safe haven on the opposite side of the country, or let them settle down eventually, build a compound of their own, making a city and a community and protecting it from outside sources.
Populace is another thing. One of the core concepts of WoD is how people interact with one another, social combat and mental challenges instead of just physcial confrontation like you're likely to find in something like D&D. A lot of apocalpyses end up with a ton of people dead, leaving you less people to deal with. If you still decide to go with an end of the world with a high body count, it would be a good idea to advance the in game timeline by a few decades. Enough so where some comforts of society have returned, populations have begun to grow again, but not enough to where it makes a huge difference. Think the TV show "Revolution" or "Jericho".
If you plan on keeping much of the supernatural material that makes the WoD so amazing, I would recommend investing in the Hunter: the Vigil books, simply for their information about monsters. Especially the suplementals like Witch Finders, Spirit Slayers, Slashers, etc. You should also make sure you have copies of Ghost stories, mysterious places, and midnight roads, as those are all great books to pull from for a Post apoc setting.
Last, but not least, Money. Money was the bane of my existence when I was making my game. It is hard to make a barter system that has any kind of regularity, but that is probably what you will end up going with. If you wish to make things easier on yourself, you have to make some kind of Money for your game that would be recognizable between settlements and compounds, as the US dollar, the Euro, and the Yen are probably worthless after the end of days, and yes, before you even say it, bottlecaps are in fact an option.
That is all I can remember at the moment, so please ask any more questions you might have.
