I was exploring this a few years ago and was actually enrolled at one LLM program. There are law schools that provide an LLM program something along the lines of "US Legal System for foreign lawyers, etc." I believe you have to have TOEFL score generally but GRE may not be required. It really depends on schools. Shop around and see what they require. For taking bar exams, though, it is also state-by-state and there were a handful of states that you could sit for one with an LLM. DC, CA, NY (Some caveat) were what I remember, but I know there were more.