Fix/replacement for v-brake part
When it's called anything, which it usually isn't, it would be something like a "spring carrier." What's going on here is fairly common to see on brakes like this. Mostly it happens when, as in the picture, the spring tension adjustment screw is threaded all the way in. Taking it out some, and then adjusting the other one on the other arm to compensate, may allow it to make contact with the spring nub rather than what it's doing now. If that doesn't work, i.e. if it's doing this no matter how screwed in it is, then taking the whole thing apart and bending the spring ever so slightly may work.

Replacement parts aren't available, although a much better complete brake is about $10US.