Widely available cassette cogs: recommendations?
11-28 through 11-46 cassettes are all pretty ubiquitous these days.

Sprocket sizes for a few cassettes in this range:

11-12-13-14-15-17-19-21-23-25-28

11-12-13-14-15-17-19-21-24-27-30

11-12-13-14-16-18-20-22-25-28-32

11-13-15-17-19-21-23-25-27-30-34

11-13-15-17-19-21-24-27-31-35-40

11-13-15-17-19-21-24-28-32-37-42

Just based on how common they are, I'd say that choosing somewhere in the range 12 - 28 teeth will be safe. However, larger sprockets are attached to a spider and some smaller ones have a built-in spacer. Fundamentally there are probably many issues with choosing to use cassette specific sprockets. You might be better off looking an single speed or internally geared hub sprockets, which do exist in non-freewheel versions for 3/32" chain as well as 1/4".

Another alternative is to look at the small end of chainrings in common bolt patterns, 22, 24 and 26 teeth are pretty common. There are plenty of 3x7, 8, and 9 groupsets around for inexpensive bikes and that is not likely to change soon. Chainrings are usually flat and can be purchased individually.