If you missed watching it in class I'm sure if you asked nicely your teacher would lend you the video? You could watch what you missed in lunchtimes and catch up that way.......if not
Try
www.ebay.com or even amazon.com
Search for: "king lear - Laurence Olivier"
You should be able to find something on those sites. If not try to see if your local video store has some or even if they know where you could get one.
If you don't want to go and buy/rent the video just go to:
www.google.com.au
and type in "king lear summary Laurence Olivier", google should sift through all the sites and look for those key words until you find something.
Good luck!