Just Grace, I wouldn't give up April comp plans just yet if you can find a suitable bit in the short term. It is really just a matter of playing it by ear. You might be surprised and finds that she goes even better in the new bit, or adapts to it very quickly.
Why exactly does she needs to work in a Kimberwick? Maybe, depending on the reason, we could help with other bit suggestions that could do a similar job.
I like the baucher as a pre-cursur to start a horse in a double, as it gives a very similar action to a curb, putting some pressure over the poll when you engage the rein further than simple contact. This is great for horse's that are quite locked or like to run and brace through the poll, jaw and neck. If that's an issue you have, the baucher would certainly be a good starting point :)