search by MPAA certificate

I'd like to find some way to search for a movie by its MPAA certificate number. This is most often found under the parents guide. For example, the entry for The Shawshank Redemption at https://www.imdb.com/title/tt0111161/parentalguide is

United States:R (certificate #33087) 

I'd like to be able to search for `33087` and get back The Shawshank Redemption. I'd really like to be able to do this as an API call or something like that.