I don't think MC reads that file attribute into a Library Field, so there's no way to query it from within MC. It could, but it doesn't.
For the record, though, testing read-only vs. read-write status is actually somewhat challenging, even in C# (I know, I've messed with it a ton). The only really reliable way is to try to write to the file or folder, unfortunately. You can query a bunch of things, but there are a ton of interlocking items that can cause a filesystem location to be read-only, and not all are easy to query:
* Read-only attribute on the file.
* Filesystem permissions on the file, or any of its parent directories.
* Network share permissions on the hosting share.
* Entire volume mounted read-only.
* Writing to the disk is physically disabled (this is, obviously, much more rare than in the days of floppies, but can happen with encrypted containers, optical discs, and disk images still).
* Filesystem corruption or errors.
Usually the simplest method is to try to write to it, and catch any exceptions thrown.
Why not just fix the entire directory structure at once? Where are these read-only files coming from?