Eyes Struggling to find pupils

A quick size comparison: 16mm, 14mm, and 8mm* eyes compared to 4mm and common #11 seed beads. Hopefully this will help!

*Corrected version

eye sizes vs beads correct by M Collier, on Flickr

Other people will probably have more info on nail gems, but for beads try Artbeads. I've had good luck with them before.

 

A good place to find options and buy them would be a jewelry making supply store like Firemountaingems.com
You would be amazed at the options available, from flat backs to faceted (pointy backed) rhinestones to actual gemstones and beads and in so many sizes at very reasonable prices. Firemountain is the name that comes to mind because I use them, but there are many to choose from. Another is Rio Grande. Good luck! I hope you post pics of your finished eyes.

 

I get mine from AliExpress or eBay. I use half-beads in sizes between 2mm and 4mm.

 

For smaller sized iris, I feel that nail art beads are better options. They are usually smaller than the ones used in jewelry making. If you prefer eyes with high and pointy dome(which gathers lights better yet doesn't fit dolls with half-closed eyes), smaller iris is much better because the dome will enlarge the center part of the eyes. From my experience the dome can visually enlarge the iris by two times. But each person make the dome differently. So the best way to decide the fitting iris size for your eyes is through trial and error.
As for where to buy them, same as Shojo-Chan I would recommend aliexpress/ebay. Ali is probably better as most ebay products are shipped from China anyway.

 

If your looking for pupil size, you can always look at the eyes on Etsy. Sellers list their eye size and pupil size on most of the ones they sell. Gives you some kind of an idea of what scale you want to try. I've also bought half beads on Etsy as well. Good luck!