If you are using free Drupal themes for your website, it can become a pain to find one that very few people are using. Rather than looking for themes that are different, you could select a theme and change it slightly.
This is not just about a change of colors or headers. You should consider making a few changes to the actual design of the theme. You will need to know about CSS and HTML coding and you will need to be careful.
There are some risks to changing the themes, which involves breaking some of the links or adding an error to the program. However, as long as you know what you are doing, it is possible and you could have a completely unique website. If you are really struggling, you could consider hiring a web designer or have a friend who knows about the coding look into it for you. It may cost money but it will be worth it when your business becomes successful.