Answer to "Where can I buy a new Samsung Galaxy S II LCD display?"The prices have dropped a little now. You can find these screens here - Samsung Galaxy S2 screen replacements Original screens from a trusted US company.
Answer to "Screen cable ribbon tear"I did the same thing. The ribbons can not be replaced as they are part of the screen. I got my screen replacement from RepairsUniverse as they are based in the USA. The parts are here - Motorola Atrix Screen Replacement They also included a video repair guide which I found useful for the installation.