I've uploaded 3 sets of .stl files, including a small, a medium, and a large iris. The size is indicated in the filename "ros", meaning "radius of outer shell" in millimeters. You need one each of the shell, lid, lever, and blades in a given size. If you delve into the OpenSCAD file, you can make any size you like.
Place one blade, flat side down, inside the main shell.
Position the blade so that it is rotated to the "open" state, with the most-clockwise gear of the blade engaged in the most-clockwise gear of the shell.
Continue placing blades like this in clockwise order, at each of the gear groups inside the main shell. Each blade will overlap the blade previously placed.
Placing the final blade will be tricky, as it must slide over the previous blade and under the first blade.
Once all blades are in place, carefully lower the lever disk pegs into the blade holes. Lock it all in place by screwing on the lid.
Open in Customizer to adjust sizes, blade count, and fillet. Works well within a reasonable range of diameters and opening sizes. If Customizer is broken, you can still use the .scad file here with the free software OpenSCAD. It's daunting at first, but easy to use if you give it a few minutes. I recommend only changing the variables in the "Global" section. When done, press F5 to preview. When you like the changes, press F6 to render, and then find the "STL" button to export your results.
If you use in a project, please share photos.