IMDB is a database that holds information on various moving image media and doesn't contain many films you can watch. However, it does link to partner sites which do provide the option to buy or stream the films. You can find these by looking on the film's page or using the filters in the side bar of lists (most importantly in this context your Watchlist) to filter by online streaming options, like Amazon Instant, Love Film, the Internet Archive, etc.
If there is no home media or streaming release then post on the film's forum expressing an interest and someone will often drop in when it does become available.
