A source for Creative Commons (not pd) classical music...

https://www.gardnermuseum.org/experience/music

These are recordings of live performances by a variety of musicians from a long lasting podcast series.

Licence

https://www.gardnermuseum.org/organization/rights-reproducti...

and scroll down.

https://musopen.org/music/performer/isabella-stewart-gardner...

I've just discovered that the ISGM library has been uploaded to musopen.org which is good as the ISGM Web page has a pretty basic search function.