Have to find one in a junkyard. Normally, I'd just search car-part.com, but this is just one of those things that probably won't be easy to communicate. Chances are everyone will think you want the instrument cluster, not the panel. Probably have to call around or visit in person.
I don't know if it would hold, but you could try using Crazy Glue (instant glue or equivalent) to glue the broken part back together. After it's glued, mix up some epoxy and use that to reinforce the area where it was broken. It might be worth trying, for the few dollars it would cost.