I have been buying the plain eyes. I use model Testors paint and paint them myself. I stick a whole bag of them (one side)in a sheet of sytrofoam and paint the iris with a Q-Tip and let them dry. I then used a toothpick and put a drop on for the pupil. After they dry do the other side. It's a little time consuming but it works.
After I make the fly I the coat the eyes with nail polish hardener. I had my wife pick that up for me.
I'm sure someone out here has a better method.