You will find some recommendations in these discussions:

https://www.researchgate.net/post/Funders_for_article_publication_charges/1

https://www.researchgate.net/post/Funding_for_publication/1

https://www.researchgate.net/post/If_you_need_Fundraising_Help_for_Publication/1

https://www.researchgate.net/post/How-to-get-funding-for-an-open-access-Journal-publication/1

https://www.researchgate.net/post/How-can-I-find-a-funding-body-that-can-pay-the-fees-of-publishing-my-paper-in-an-open-access-journal/1

https://www.researchgate.net/post/funding_grants_to_publish_our_scholarly_article/1

https://www.researchgate.net/post/Seeking_help_for_funding_to_publish_a_research_paper/1

Consider applying for fee waiver to the journal