What fraction of Verditius magi are in one of the relevant confraternities?
Some Verditius magi band together in confraternities, small groups of like-minded individuals who follow a path formed by an earlier, charismatic magus.
So we're talking about only "some" rather than "most" or "many" of 74 magi split between Confraternities, which are "small." And which Confraternities? The most generally useful one (wooden wands) due to ease of transportation (weight but also laws) is Himinis the Mad, known for curses! I got the feeling from reading that it's not super-popular and that generally people would worry about buying from them, so maybe 2-3 magi people would be worried about buying from. The Confraternity of Roland seems to have a few more members (so, maybe 6-7) and an item. And now take into account that those initiated into Inner Mysteries are not the youngest of the magi, but moderate to more powerful. Combined with some strong Mysteries only they get, and that places a bunch of them among those who we've already counted as specializing in the high-end items for better profit. How many does that leave?
Meanwhile, there are a "large number" of Schools of Sebastian (from within a House of 114 magi) which grant Minor Focus. If my "small" number above was around 5, this would be, what, 15ish? Sure, many of those won't be as useful broadly. But even just two of them being canonical Minor Foci like "wood" or "arms and armor" with a parens and a young mage to make it a "school" would make 2 magi who are far more broadly able to apply their Foci than with "wooden wands" and 2 magi who are far more broadly able to apply their Foci than with "swords." And then there are all those others who are being given Foci that could be applied in more limited ways.
So just like Verditius, there are other places people pick up Foci they weren't born with, and quite a few of these magi could have even more broadly useful Foci.
And then there are all the other non-Tremere magi who haven't been counted so far. How many of them have broader Foci than "wooden wands" or "swords." We've seen examples of "wood," "clothing," "arms and armor," "metals," "stone," and maybe more.
This is why I said what I said about Lesser Enchanted Devices, having taken into account those Mysteries. We have to go beyond those Mysteries existing to really make those Verditius magi more likely. For example, suddenly the Confraternity of Himinis the Mad becomes super-popular and no one's worried about buying cursed items from some sort of Grand Tribunal ruling and House Verditius agreement, so now we've got lots of magi getting Foci in "wooden wands."