Congratulations on finding a Victor III. Those are such nice phonographs--nice big horn, good motor, and an Exhibition soundbox that, if rebuilt properly, can sound very good. I have one salted away in the collection--it's probably my favorite machine to casually play records on. Just go by and throw on a disc. It's so simple to use and the parts have a heavy, satisfying feel to them...
The guy you need to talk to is on the forum here. His name is Mr. Don Wilson and he goes by donniej. The records will not be original copies but they will be new ones.
You see, Scott Joplin recorded a few tracks in 1916 before his death the next year. Unfortunately for phonograph collectors, he did that work on a player piano instead of a phonograph record. The piano rolls were the "reproducing" type, and through a very complicated arrangement in the machinery, they were able to reproduce almost every nuance of the original performance.
As Joplin was ill from the syphilis that was to end his life he was not able to play at his peak, but through a process known as "Connorizing," an early form of digital re-mastering, the workers in 1916 were able to adjust his recorded piano rolls to get the true Joplin sound back.
Don Wilson runs Wilson Laboratories, and they re-make vintage formats for the talking machine. He has a catalog of records going back into the 1890s and is very good at molding them in modern resins hard enough to play on your Victor with a steel needle. (Please change it after each side, of course.) He also has record cutting equipment, and has re-released Joplin's "Maple Leaf" and "Entertainer" rags in 78rpm disc format.
Unlike the old horn processed acoustic records of yesteryear, his were done with microphones and good amplifiers, and sound wonderful. The price is worth it. And since he recorded directly from a player piano, it is as good as having Joplin back from the grave to play for the phonograph one more time. Not bad talent scouting considering Joplin has been dead since 1917.
So to play Scott Joplin, that is what you need to do.
