Answer
- Goto the OPeNDAP Dataset list (add your own server)
- Search the GCMD using their special interface for OPeNDAP.
- Tasmanian Partnership for Advanced Computing Oceans and Climate Digital Library Portal
- The THREDDS server at Unidata
- Use Google to search for words/phrases that typically appear on DAP server pages. These include 'OPeNDAP Index,' 'DODS Index,' and 'THREDDS Data Server.'