Is it easy to get replacement parts for SR5 4runner2007 or 2008 V8?

as for the v8, there will not be a problem getting parts as they used that same v8 in the several of their models, 4runner, land cruiser, tundra, Sequoia, and also lexus gx470, lx470, so it is still very popular motor. but for what your describing, the v6 will be fine for you. still plenty of power and better fuel economy than the v8, also less weight. and if you run into a step hill or any other sticky situation, you still have low range and that will always be more power than the wheels could have traction even if all on dry pavement. My v6 4Runner has 281k miles and still runs like new.