Everyone seems keen on pointing out that Season 8 is only in comics, but I have a feeling you knew that already.
If you want to know where you can access it online, there are a handful of torrents you can download, I've heard, where people have scanned the images and you can read them that way. Don't ask me where to find them, because I don't know.
The series has been put into five volumes of paperback "graphic novels" (five so far, more to come). You can buy these anywhere, including Barnes and Noble and Amazon.Com. I would recommend Amazon if you don't want to spend a lot of money, because you can get them very cheap from second-hand sellers.
However, I buy mine from Barnes and Noble brand new, to expand my collection. I also purchase Angel: After the Fall, and I have the two Firefly volumes as well (I'm a geek, what can I say). It helps that I have a B&N discount card. Anyways, I highly recommend checking out Buffy Season 8. VERY worth it, and it just keeps getting better. Angel, on the other hand, is great through volume 4, but "Aftermath" (Volume 5) is a little weak. Your decision, though.
link for "The Long Way Home" (Volume 1).
link for "The Long Way Home" (Volume 1).
Shop around and try to get the best price.
Happy book hunting!