Finishing Sous-Vide Chicken Thighs en masse
You could use a searzall with the chicken on a large baking sheet (make sure you have adequate space to do this without accidentally setting anything else ablaze). 

I usually use one in conjunction with pan-searing, so I'm not sure it could do the total job for you, but you certainly could use the broiler method and then finish up with the searzall (or, slower, any culinary torch) to get the sear that you want.

Outside of that, a gas grill would probably be your best bet.

Bonus: It's a torch. Torches are fun, and possibly a neat way to entertain your guests.