Common Data Set. It's a document that each college (should) post online. In some cases it may be named something slightly different - call the school and ask if you can't find it.

Imo it is the most valuable of research materials for picking colleges.

What's CDS?

I don't know of a registry. You can often find this information in the CDS of each school though. You usually have to do a little math (i.e., the data will have the #of OOS that applied, and the number of OOS accepted, and you divide accepted into applied to get % accepted).

That's the OOS acceptance rate.

If you're looking for the % of current students that are OOS, can usually find in the CDS or in the enrollment data in College Navigator.

Is there a registry for % of OOS admits for flagship state schools? Trying to see if there's a portal that can provide this info for all state schools.