Buying Comics After Release

[leesalogic]

I read the Redirected Male and Read This or Die articles from Sequential Tart on Buffy, the Vampire Slayer, Season 8. I am considering buying these since it's a 'verse I'm familiar with, or will be when I finally finish watching the TV series via Netflix. I won't want to read them until I'm done with the TV series either (I just like to watch/read things in sequential order), so this could be several months away. How do y'all buy past issues of comics? I went to Amazon but it looks like they don't have them at Amazon and I'd have to buy used from their list of folks that sell used.

Will these eventually be published in a big novel format like the Sandman Volume One series?