I often see people say stuff like "I'm going to buy X now and then buy another in a year or two to SLI/Crossfire. But when I search on sites like Amazon or Newegg they rarely are selling cards that are a year or two old. In my case I like the idea of buying a GTX 770 right now, and then adding a second one in the future, but I'm concerned that there won't be a reliable way to obtain one. So where do you guys get them?