difficult question. s.th. there is a charity/trust that was founded to collect orexhibit certain manuscripts. however, most of the time they have no jpgs on theinternet. a good start could be:pierpont morgan library, n.y. (they have lots on mahler, some mozart, beethovenand schubert, even an autograph of listz's mephisto waltz).https://www.morganlibrary.org/collections/collectionsThumbs.asp?id=Musicthe british library (e.g. haendel, mendelssohn, etc.)https://www.bl.uk/collections/musiccollections.htmllibrary of congress (might also be a good starting point)https://www.loc.gov/beethoven haus bonn (beethoven museum in bonn, germany)https://www.beethoven-haus-bonn.de/sixcms/detail.php//portal_enpaul sacher foundation basel (largest collection of contemporary music)https://www.paul-sacher-stiftung.ch/e/collections.htm (only for professionalmusicians or scientists )wiener landesbibliothek (for autographs of schubert, strauss family, etc.)https://www.stadtbibliothek.wien.at/index.htm (but no pictures )
I don't know if Kirkpatrick actually edited all 555 or so Sonatas. The only ones I know of are the 60 published by Schirmer. I would however love to see all of them edited by him.