YZ400 said:I checked and it is made by Buck Chuck.
It would be a good idea to have the specs for a jaw handy - scroll pitch, jaw width, slot size and height, etc. Buck has have several different models of the 5" 3-jaw chuck and the jaws aren't necessarily compatible between them. As an example the chuck below is a 5" Buck but very different from yours.
I've got some spare jaws in the shop, if you list the specs I could go through them and see if I have anything close.