I am currently working on a project and need to log pressure from a tank. All the transducers I can find are either not high enough pressure, not threaded right, require too much power, or just seem too big compared to whats found in dive computers, and I really doubt that they use the most expensive parts.
I expect they have the actual fitting custom-made. As in, the sensor you can buy for a couple of cents, but you need to put it into the pressure-proof body that either connects to a hose and houses the entire computer, or screws in to HP port and houses the transmitter and battery and the coiled antenna etc. I doubt you can actually buy the "sensor and body", if that's what you're asking.