Interesting.
I've been a reader and regular participant on TFL for years, and don't remember that message chain. (And since I have a pre-B I would be paying attention.)
I just did a lengthy search of "parts" and "CZ-75" there, as well, and found nothing.
I know of no problems with parts availability -- primarily because I haven't heard of any parts failures with the pre-B guns. (Not to say they don't have them; just to say there are so few floating around, and so few problems, we just don't hear of shortages, etc.)
As FEG notes, many of the parts are interchangeable. And with the few that aren't -- hammers,for example, and some slide stops -- the newer versions will typically work in the older guns, but not vice versa. Witness parts may also work for some things.
You've asked a good question -- and I don't think we have an answer, yet.