Ask HN: Are ISFET/BioFET devices available to the hobbyist? Why not?

As far as I can tell, Ion-Sensitive Field Effect Transistors (ISFET, cf. MOSFETs) and BioFETs (aka 'biosensors') are not commercially available, at least to the amateur/hobbyist.

Are they only made to custom order, with a specific device in mind?

MSFET3330, for example, is a pH-sensing ISFET. But searching for that part number nets me very few results, none of them selling me one.