The Kiwi's really are the experts...rotationally grazing grass finisher's under irrigation. It takes a combination of beef genetics, the correct forage chain, and good management. The biggest stumbling block is processing, though. Back east, there is a dearth of medium to large scale processing that brings in enough throughput to maintain margin for everyone. Out west, I've heard it's more about creating enough volume (through co-ops, usually) to get a big processor to devote an entire line strictly for grass-finishers, even if it's one day a week. White Oak Pastures has built their own USDA small scale processing plant on farm. (both white meat and red meat, separate). A few years back, JBS bought Grass Run Farms to get into the game, to try and scale up production and grab marketshare of the booming growth in the industry. Not sure how that's working out. I believe they were attempting to create a feedlot environment (bringing stored forages, albeit without grain, to the cattle to lower costs and maximize production).
Hickory Nut Gap farm in NC. is moving a lot of regional beef, as are Seven Sons, in IN, and Winecup Gamble, in NV, among others.
I patterned my finishing system after the Kiwi's grazing dairies here in GA, but got discouraged working with some of the national wholesale branded programs and their unwillingness to create long term relationships. I now sell seedstock into the growing grass finishing sector, and just market a few open heifers directly. Feel free to PM me if you have any specific questions.