I was surprised that this doesn't seem to be the case - For example, I can't find any pH sensor on Adafruit. There is a model that's easy to find on eBay or Amazon, sold under various brands - I was unable to get this working, likely due to documentation or software issues.
I'm using "Aquarium Hydroponic PH Electrode Probe/Liquid PH Value Detection Sensor" on ebay for $36 with probe. It even came with example code.
I'm using it for a basic application and only roughly calibrated it with paper tests using tapwater and vinegar. I'm only measuring between ph 5-8 and my application doesn't really require precision.
I picked this sensor somewhat randomly on Aliexpress and it seems to work well (with calibration on both, tracks closely to my commercial Nutra-Dip Trimeter).
For hydroponics (where 0.1 pH is plenty of precision and pH range should be inside 5-8), I was quite happy with the $14 version below.
