If your existing switch is the old-fashioned kind that uses a bimetal
spring; you may be able to "recalibrate" it by rotating the mounting post
for the spring.
Or if it uses a bimetal spring plus a mercury switch, just mount it on the
wall crooked <G>
I did some quick searching, but everything I found either wouldn't go that
low, or cost over $100.
Here's one that will go down to 39F, though (and might be modifiable to go a
bit lower, as above)
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