Online Community of Zenith Builders and Flyers
Years ago, I got mine from Steve Rance in the U.K. I haven't found his contact info yet but I'll look some more. The LAA (Light Aircraft Association) in the U.K. probably has his contact information.. Seems I've seen an ad "somewhere" for a U. S. TOCA but don't remember who the vendor is.
Taping over the oil cooler and closing in the cowl openings has a long winter tradition around my airfield. If the weather suddenly warms up you simply pull some tape. or add tape if it gets colder. You can always land and adjust enroute. I know that was not answering your question, I was just defending a winter tradition (LOL). KISS principal rules.
Found 2 email addresses for Steve Rance:
Also, here's the drawings and approval of the TOCA design from the LAA in the U.K.: Thermostatic Oil Cooler Adapter
As I understand it, in the U.K., the LAA regulates - under approval of the CAA/Civil Aviation Authority - experimental and homebuilt aircraft designs and modifications, so the TOCA is an official, "approved" design.
Typically, Steve would manufacture these in small batches and then make more when they sold out. Hopefully he still has these in production and/or has some stock on-hand.