Hi Rosalind,
Unfortunately, there is currently no such API. You need to either request posts one at a time, or fetch a page of posts in order.
If your code is taking too long to run, you may want to try parallelizing post lookup requests to the API. You should be able to make at least 10 simultaneous requests without much overhead.
Looking up multiple posts on a blog is a good idea though, and we will keep it in mind for the future.
Regards,
Mike