Looking for natural gas burners

Hey All, I'm looking to aquire some natural gas burners to upgrade my system ( or more honestly to actually start buidling a " system" , instead of just a mish-mash of equipment) I've seen some stuff on boring out a propane one to make it work, and am considering that option, but would like to try and go the more conventional route first. If anyone has 1-3 of them for sale, please let me know.