How much of the coil was taken when it did break?  If not a whole lot, you could possibly make a new end for it and it should work again.  If too much was taken, you possibly could take another  spring from another typewriter or some other machine that has one of similar thickness and remake a spring.  The spring on the machine in the picture looks like a pretty simple affair, and you should be able to make another spring for it no problem if worse comes to worst.