1. The Hymnary.org: This website provides a large collection of hymn texts and sheet music, including "Bless Thou O God This Day." You can find it by searching for the hymn's title or composer.
2. Hymnary.com: Another online resource for hymn sheet music is Hymnary.com. You can search for "Bless Thou O God This Day" and find several versions of the sheet music available for download in different formats.
3. Musicnotes.com: This website offers digital sheet music for purchase. You can search for "Bless Thou O God This Day" and find the sheet music available for immediate download.
4. J.W. Pepper: J.W. Pepper is a music retailer that also sells sheet music. You can search for "Bless Thou O God This Day" on their website and find both physical copies of the sheet music as well as digital downloads.
5. Local Music Stores: You may also be able to find the sheet music for "Bless Thou O God This Day" at your local music store. Check the store's inventory or ask the staff for assistance.
It's important to note that some sheet music may be copyrighted, so please make sure to respect copyright laws when using or distributing the music.