True but they have always been extremely rare..
No RPO Z11 409/427s were sold for street use.
GM pulled the plug on factory sponsored racing efforts as it was being developed. Fewer than 50 cars were built with the engine and sold to drag racing teams. Another 200 or so engines were sold across the parts counter.
In 1968 I bought a Z11 camshaft throught he parts department at the Chevrolet dealer where I worked for a friend of mine who put it in his 409/425. IIRC, it cost $24.**.