Type "old movies" or the particular titles of the DVDs you wish to buy into your search engine; this search should come up with a number of online DVD stores. Browse these stores and choose a site, which sells the old movies you want and sign up to it. Order your chosen films from the online store.
Download a media sharing program, such as iTunes or Windows Media Player. It allows you to purchase and download old movies. Download your chosen movies to you software program and either watch them on your computer or burn them to a blank rewritable DVD disk.
Look up your local secondhand film stores in your local directory. Visit them and search for the old movies you are looking for. Alternatively seek out any local jumble sales or car boot sales; although not guaranteed, these sales usually have a wealth of people selling old, used movies.