I'm not 100% sure if these will work for your situation, as I have no clue how well/far apart they work aside from my experience in crit racing, but these are what my team uses: Radios and we have them paired with these earpieces.

I will caution you that while wearing the radio for the race looks cool, and feels pro, they're kind of an annoyance and pain in the ass to keep in place and keep in your ear the whole time you're riding.