Ion-Sensitive Field-Effect Transistor Help

I'm doing some research on different PH meters and ISFET's keep being mentioned. They seem like a great alternative to the bulky glass probes that are most common and I know they're used in higher-end PH monitoring equipment.

The problem is that I can't find them for sale anywhere?

I've Googled quite a bit [mostly scientific papers pop up]. I'm starting to wonder if they go by a different name or there simply isn't a market for them for some reason?

I'm fairly confused, if anyone has explanations or info/experience with these, I'd love to hear.

Thanks in advance!
-Chase

So the plot thickens...

I found this obscure book source that says, in the United States, they are only manufactured at the University of Utah, Salt Lake.

Are these things so difficult to manufacture that the medical device companies gobble them all up before any of us DIY'ers can get our hands on them?

Are they prohibitively expensive?

I really am stumped here...