I found plenty of thermostats with this design but they were longer, shorter, bigger in diameter, not offset from the center-line like the ST's is or they did not have the little bubble flapper thing. Usually there were two or three things not quite right. I scoured the inventory at Kragen, AutoZone, Pep Boys and NAPA. I looked at t-stats made by Prestone, Stant, and another manufacturer who's name escapes me at the moment. I've examined literally hundreds of cage t-stats and come up with nothing close enough in physical dimensions or features to be comfortable with. Then there is the additional requirement to match the temperature rating (82C or 180F).
The only thing I haven't yet done is try a Honda cage dealer. If they turn out to be available there I wonder if they will be any cheaper than the $22 price I found at Zanotti Motors for the OEM. Some of the cage t-stats I looked at were over $40.