Quite a few are up on Ted Tjaden's site, which has a ridiculously impressive collection of sheet music and information. Many of these are particularly hard to find, and haven't yet made their way to the IMSLP Petrucci Music Library, so Ted's page is a great resource. In addition to classic rags, he's also compiled an impressive list of ragtime's predecessor, the cakewalk. Ted writes:
Although the American cakewalk dates back to the early days of slavery, the cakewalk as a distinct music and dance style had its formal beginning in the 1870's and reached its peak of popularity at the end of the 19th century and early 20th century. Unlike classic piano ragtime, cakewalk music was meant to be danced to and often performed by a small orchestra or band. Although cakewalks were generally lightly syncopated, their melodies and harmonies were generally not as sophisticated as those found later in the classic rags of Joplin, Scott and Lamb.
If you're like me and foster a healthy (I swear!) infatuation with this sort of old music, I urge you to take a look!