Most people have heard of the Petrucci Music Library, otherwise known as IMSLP. But have you come across the Internet Archive, at https://archive.org/?
They're really useful. Don't assume they're only for printed texts, either. Today we were looking for a vocal score of the opera, L'Inganno Felice, by Gioacchino Rossini. We found an old edition in the Petrucci Music Library. (See here.)
We checked Archive.org, and there was a solo piano rendition in all its early 19th century splendour. (It's dated 1812, to be precise.)
So you see, these sites are useful, you really should favourite them! Save to your Diigo account and you'll be able to access them from any of your digital devices.
Staff and students at the Royal Conservatoire of Scotland also have access to Library Music Source via our database page. It's only accessible on-site, but it's another valuable source of performance materials.