Are you sure about the 'just came off' aspect? There's a big scratch between the cable stops and another on the opposite side of the broken stop.... almost like something impacted that area.

If you can't find a clamp on stop
and you don't mind appearances

take the barrel adjuster from an old shifter or caliper brake
strap it to the frame with a big hose clamp
bonus point if the hose clamp rests against the remains of the old cable stop; to prevent sliding
-dont try this on brake cable stops; shifters only