I don't think it is online. It might be on a DVD as a special feature. From what I read in the Making of Superman book, she didn't get the part because she didn't make a good impression on Christopher Reeve with her odd behaviour:
"The producers were still embroiled in casting problems, the most crucial of which was finding the right Lois Lane. (At lunch one day, Chris told of how he had been reduced to speechlessness when Susan Blakely, fresh from her screen test for the part, sat down to chat with him, removed her chewing gum, and stuck it to the bottom of one of his shoes.)"