The biggest gravityfed smoker I know of is the Stumps XL Stretch. That MIGHT be big enough for a small restaurant.
2013 Stumps Classic - Delivered 4/15/13
Large BGE - Rescued 2012
2010 WSM 22.5"
2010 Weber genesis gas grill
Rescued 22.5 Weber One-touch gold
BBQ Guru CyberQ
2011 Built UDS - Retired