Very nice find! These seem less common than clear versions by far.

Nice! Yeah diffused HPS lamps are rare because they're more expensive, have fewer lumens than a clear lamp, and coated lamps mess up the optics on asymmetrical lights such as cobraheads and flood lights. But personally, I think coated lamps are way better in a bucket light type fixture because the glare is just so harsh from a clear lamp in a bucket light.

Or any other symmetrical application...