OpenCPN uses standard GPX files. So, tracks from any
gps or
chartplotter should
work fine. Wherever people in the area you are in decide to share them, I have no idea. I don't think sharing tracks is very popular. Maybe if you share the areas you are interested in someone local to that area can chime in.
My suggestion for areas not charted well is to use SASplanet and make
charts from
satellite imagery. I hit a reef following a track that was "guaranteed" to be safe. So, I would never trust a track from someone I have never met.