I am looking for a NEMA head refractor.

Sometimes they show up on eBay, I haven't seen any right now. But they can be a bit pricey. There were some really nice brand new GE ones with smooth reflector and clamp band refractor, but I think they all sold. Also have seen Cooper and AEL sometimes.

It's actually sometimes better deal to get a NEMA kit and use the refractor, then can get lamp, photocell and arm, and extra head for not much more sometimes, than just a refractor.

Update, the GE ones are actually still available $33. Shipping is free though and these are really nice, have a safety chain and all.

GE Refractors