Some producers (like Hitoshizuku) have official websites where they upload their instrumentals, and some put them in their albums (on iTunes and such). I believe some have those (as well as lyrics) on KarenT as well. Another option would be instrumental covers, remixes or acoustic/piano versions. Lots of YT channels upload off vocals, though most are downloaded from piapro as well.
If you have some songs in mind, I can try and help you find instrumentals!