I don't understand exactly what you have in mind, but I have the "Daily Ukulele" books and they are already ukulele friendly. I mean, if you are just looking for ukulele songs to play, they work well for me. Also, if I have a specific song that I want to play, I use ultimateguitar.com if I'm just looking for lyrics and chords.
I do that with piano sheet music all the time. I mostly use musicnotes.com (which will transpose the key for you - yes, I'm that lazy!), fake books, and vintage sheet music found on eBay.
A good selection of tunes (over 500) that'll fit well onto a ukulele can be found in Jack Campin's "Nine-Note Tunebook" at http://www.campin.me.uk/Music/Chalumeau.abc . These tunes have been selected/arranged specifically with the basic chalumeau in mind, but they're absolutely fine as written for the ukulele as none of the tunes play below "C" (third string open) or above "D" (first string, fifth fret). Much music of a similar standard, albeit possibly with a slightly wider range, may be found in many collections for descant recorder, this being a "C instrument" as well, or indeed in many collections for whistle (tin whistle/penny whistle), which are usually written for a "D" instrument. John Tose's collection of Welsh-orientated tunes for the pibgorn at http://www.mochpryderi.com/Resources/Tose 200 Tunes.pdf will also be suitable, the pibgorn being an 8-note pipe in "D".
Hope this helps, but if you have more specific requirements, please say so
If you like old jazz and pop tunes, especially from the 20s to the 40s, i recommend the PDF digital collection of sheet music Ian Chadwick put together. The melodies and harmonies are accurate. Ian posted previously on this thread. His collection is a treasure trove. I have lots of his music on my ipad.
For music after 1923 until fifty years ago, you might find sheet music scans at the National Music of Australia digital music collection. http://www.nla.gov.au/what-we-collect/music
These sites are scrupulous to obey copyright laws; hence the limitations. Australia has different copyright laws, though they'll probably cave soon to the preposterous international extensions we can thank Sonny Bono for.
Most of the sheet music doesn't have ukulele or guitar chords, but music close to the 1920s might. I occasionally trip across uke chords in a stack of old Chemnitzer concertina music I bought, so they do turn up where you might not expect to find them.