Cable Stop For Internal Cable Routing
As all the comments have stated most appear to be brand/ model specific. Since it is an older frame it is possible that it didn't have them. Some older frames snaked the entire cable housing thru the frame. The stop was on the component, (brake, derailleur or frame mounted cable stop). If you search for custom bike frames builders you may find some local sources. If you don't have your heart set on internal cables, you can use bolt on frame mounted stops. You will need to measure the frame tube diameter and figure out if you need single, double or triple stops.