NatiS Hi Natalia, welcome!
Although @Dmitry has already replied extensively, let me link for you this recent publication directly from The Open Mic regarding sample translations and how to get them https://theopenmic.co/sample-translations-how-and-where-to-get/ This way you can get to know more and also comment to ask the author any questions, if you'd like
Generally speaking, if you have signed a NDA upon starting a collaboration with an agency, you may not disclose any information about end clients, and that includes portions of texts. Check if there are agencies which haven't requested you to sign anything - it happens more frequently than you'd think - and in that case you should be good to go.
I also happen to know that the portal TM Town offers texts of various subjects to be translated as samples. Of course you must be a member to access this service.
As to references, I'm afraid you cannot put the end client's name on your website, but you could definitely ask agencies for feedbacks and comments on your work and then insert quotes. If you receive feedback through Proz.com and have clients which have expressed their willingness to work again with you, you can link that corresponding Proz page in your website ?