I am seeing only 2 on the AAMC website but I often see study plans and other online resources that say that there are up to 8 official practice exams??
There are only 2 AAMC scored FLs, although a third one is coming this fall. There's also a sample test from AAMC that only shows percentages and not scaled scores. So as of right now, only 3 AAMC tests.
The "8 practice exams" you're seeing is a reference to the "old" (pre-2015) MCAT, by the way. Those resources are no longer available (and are in the format of the old MCAT anyway), but a lot of their passages have been folded into the current AAMC Question Packs.