It's a niche market. Kirkham seems to produce a Cammer Cobra every now and then, it's a popular engine for their clients that want to go crazy. But a brand new SOHC will run you about $40-50k, so it's understandable why you don't see them all the time in projects.
Am I right that Keith sold Keith Craft Performance Engines? I know they used to advertise a SOHC engine build all the time on eBay, with Coon heads. That always made me think that Coon must have made sure he didn't screw over Keith...