You haven’t mentioned what you need it for but if it just for a list, I’d use the default functionality in both console (“Applicable computers” tab in the baseline) or in Web Reports (just find the baseline via “Explore Computers” -> Content and click on the baseline, it will have all the details of both “still relevant” and “remediated” machines). If it is for some kind of API-based data retrieval, something like this should do:
names of applicable computers of bes fixlets whose (baseline flag of it and (name of it = "BaselineName") and (display name of site of it = "SiteName"))
