How to get a list of ALL LOCKED FILES (i.e. in 1 single window of a complete disk)?

On Mac OS X 10.11 (El Capitan) I wanted to changed ALL MY (7) FILE-LABELS

(now called TAGS). I've about 50.000 documents in about 1000 (sub-) folders

but can't change them all in one go, cause there are some (500? 1000?) locked files.

How to find ALL locked files amongst a complete disk?

After, fortunately, El Capitan allows me to unlock them all in 1 go, so… it's just to FIND THEM!