are you looking for 50k pages that can collaborate with your brand or do you have a 50k and you want to get some brands to work with you? in both cases DM’s should b a good start, you can use Jarvee to scrape the data (pages, brands) that you can contact, the ones that you think they might be interested and then DM them.
Jarvee has a lot of filters that can help you with the scraping process you can check that and see how it goes