Ask around and do internet research. Firms will usually have bios for their partners on their websites which will give you an idea of their caliber. Find the firm that has partners with SCOTUS cases under their belt (preferably winning them), or winning cases for 9 or 10 digit estates. They may cost >=$1000/hour but their skills and network are priceless when you need them.

You don't need a connection to get a foot in the door with them but it doesn't hurt.