Very doubtful, but as you said you should easily be able to make one yourself out of whatever material is available to you. Steel, aluminum, tin, plastic, whatever. In fact, it doesn't even need to be a full bracket. Two strips mounted to the case at the right level to match up with the mounting holes on the fan and drill a couple of holes to mount the fan, then screw the strips of metal to the case.
You could also try and adapt something like any of these:
https://www.amazon.com/AC-Infinity-...se+fan+mounting+bracket&qid=1596441109&sr=8-3
https://www.amazon.com/Bitspower-Un...se+fan+mounting+bracket&qid=1596441109&sr=8-4
https://www.amazon.com/Beioust-Radi...e+fan+mounting+bracket&qid=1596441109&sr=8-25
Etc.
Much like I did with my old Cooler master Storm enforcer several years ago where first I just cut out part of the case that interfered with airflow and mounted it directly to some metal strips.
But then later on took it a few steps further with some actual modifications.
OH boy, I have a lot to tell you
I saw your suggestions, it barely came handy to me and the cost of it was like 18$ for only a universal tank brackets, when I saw that price I said hell no, no way.
So I took the idea of it, As I modded the case I removed the big classic hard disks bay, it's a huge piece of metal inside the case, I measured the sizes I need out of it, drew it on paper to feel like it's legit, it's like a clone for the mount brackets for the other fan I showed you.
But the problem is I don't have the tools to do cuts professionally on aluminum (same case material) so I dropped this idea entirely.
Instead, I went to a Smith workshop thought of cutting a slide of that aluminum piece, drilling holes in it and inserting screws to make it fit,
And it did! it's so powerful holding and so clean its impossible to notice:
View: https://imgur.com/a/jdmvvxi
that's basically how I managed to make it, took me so much work, drilling on small pieces is a pain, lots of drilling so the screws fit everywhere.
Also one of the mounts bottom left, I was making it while drilling it broke because it's too small, so I just ignored it.
The arms (I call them that) are holding so strong, a friend told me the fan might shakes for instability? But it's mounted so strong, I don't see any issue, right?
Thanks on suggesting your ideas!