LinkedIn is a free service for professionals that you can leverage to connect to other professionals of your field.
How do you find clients? You can of course call translation agencies or companies by phone or send them an email to figure out if they are interested in your service. In most cases it is easy to just go to their website and find their contact information.
However, it is a bit of an effort if you want to contact many companies/agencies and this is where LinkedIn can be a great help. A lot of professionals of the localization field including translation agencies (LSPs: Language Service Providers) are on LinkedIn and you can reach them all at the same time. And in addition those companies/agencies can find you as well to ask you for your service.