I need an answer in reference to 14 CFR 23.207. I looked there and couldn't say 100% if it was a yes or a no.
No, many aircraft don't have them, like the Cherokee since it uses a gear warning horn. The horn signifies that the gear isn't down and you don't want to confuse that with the stall warning, so they don't have one.
23.207 says that an audible or visual indication is not required as long as the aircraft exhibits a "warning" 5 knots before the stall, in the case of the Piper Comanche the warning that satisfies the requirement is the stall buffet.
The relevant section of 23.207 is part (b):
(b) The stall warning may be furnished either through the inherent aerodynamic qualities of the airplane or by a device that will give clearly distinguishable indications under expected conditions of flight. However, a visual stall warning device that requires the attention of the crew within the cockpit is not acceptable by itself.
So the stall buffet, as long as it is pronounced, is adequate indication of a stall to satisfy 23.207.
The answer above is just flat-out wrong. It makes no difference whether or not certain airplanes have them or not when it comes to airworthiness.
The real answer is it depends...
91.205 does not include a stall horning but that doesn’t mean the Type Certificate Data Sheet for the plane you are piloting contains something different.
For example, a Cessna 172’s TDC (3A12) explicitly states that a stall warning horn is REQUIRED for the plane to be, well, a Cessna 172. Therefore if you are about to take off in a 172, you technically need an operational stall horn to be airworthy.
Generally speaking, you need to consult 91.205, the TDC for the plane, any STCs (supplemental), and then the MEL from the POH and probably in that order.
I highly recommend listening to the Max Trescott’s Aviation News Podcast episode 151 on airworthiness where they go through how to determine if a piece of equipment is required or not (hint: they talk about the stall horn!).