Given a team that has a project, there should be a way to retrieve the list of all repositories in that project from the API. I suppose I would expect it to live here (though maybe that doesn't make sense given the fairly 'flat' structure that the api seems to have):
https://developer.atlassian.com/bitbucket/api/2/reference/resource/teams/%7Bowner%7D/projects/%7Bproject_key%7D

Thanks!