Yeah, I've had that happen a couple of times. It's not my favorite thing. Both the Cubicle and SpeedCubeShop sell replacements. I think SCS is a bit cheaper, it was about $5 for me (in Montana) including shipping.
SCS sells replacement parts, but I'm pretty sure the cubicle only sells replacement parts on their old website, or at least that was the case when my 4x4 popped and then my mom came in a vacuumed up one of the internals. That vacuum really sucked.