Give us a little more info on the bow. Bear bows usually show the AMO length on the riser below the grip portion, along with the draw weight at 28" and the serial number. They generally also have the model: Black Bear, Grizzly, Kodiak, etc. on the belly of the bow (the side that faces you as you shoot).
Vintage Bear bows were designed for B50 Dacron string, as others have mentioned. Since you are new to this, I'm going to assume you won't be making your own string. There are several excellent string makers on this site and if you provide them the information I listed above, any one of them can make you a great string for your bow. LBR and OliverStacy are two that come immediately to mind, but I think there are others as well. You could also check the pull down menu of sponsors up at the top of this page.
Welcome to the addiction, by the way!