I've been exploring the possibilities in importing new samples to create waveforms. The John Melas Waveform Editor, which I have as a demo version, allows the import of samples (key banks) in a variety of formats including SoundFont. Have other users found sources of musically interesting samples to import and play with? I'm open to ideas! I'll buy the Editor if I know it will be useful in this.
I would start with google.
Can't vouch for any of these, but to get you started with my search results ...
https://www.kvraudio.com/forum/viewtopic.php?t=526555
https://forum.cockos.com/showthread.php?t=279893
https://www.reddit.com/r/lmms/comments/pm4z0m/list_of_free_virtual_instruments_sfzsf2/
... and so on
Search term used: "where do I find interesting free sfz samples"
Current Yamaha Synthesizers: Montage Classic 7, Motif XF6, S90XS, MO6, EX5R
Try the BBC (yes, that BBC, as in British Broadcasting Corporation).