Lovely machine. open the slide plate and be sure the bullet/shuttle bobbin is in there. It probably will be since it is in a home setting rather than a shop, but best to check.
Whatever you purchase, don't take soap and water to it, it will silver the decals.
welcome to the board from SW Washington.
When I started looking for a treadle I settled on looking for a Singer, and one that took a standard round bobbin as parts and needles and bobbins are still readily available and the bobbins hole more thread than the shuttle type.
Hopefully someone will come along with a Davis and say if the needles are standard, or hard to source.