Weird, I have the Izzy repo and it doesn't show up.
Thanks for the link!
This is a major issue with F-Droid. I can find this via a browser, but the F-Droid app doesn't show it, even searching by name. It just doesn't exist. It happens all the time, I'm not sure why it doesn't show apps that I know are there.
I can find it on Droidify no problem and after reading your comment, I also tried on F-droid app and I can see it there as well. Maybe you don't have it configured properly.
It comes up if you type "oss" and look down, as "OSS Document Scanner." But if you go past the oss like "oss sc-" it says it can't be found (because you omitted "document"). My bet is this explains why he can't find it.