Long time reader, first time poster.
I can confirm the Kowa 16-S has a rear lens thread of 43 mm.
I too am amazed at relatively how little there is on anamorphic lenses given their popularity, but I did find this wiki that attempts to catalog many different lenses, but you'll notice it's somewhat lacking in details:
http://super8wiki.com/index.php/Anamorphic_Lenses
HTH