The following site seems to have it:

http://geraniaceae.com/cgi-bin/listPlants.cgi?major=Geraniums&minor=Borders%20and%20Bedding

I don't know if my experience is just a fluke, but three times in different years I bought a G. psilostemon plant. They came as blooming plants, around 9" tall. All of them bloomed nicely through the summer, then kind of faded away and never came back. As a last resort I bought seed, I think from T&M. Those plants were small seedlings the first year. The second year they were the same size as the plants I bought, but they did not bloom. The third year they came back bigger, bloomed and stayed. Volunteer seedlings from those plants followed the same pattern. I am in Ontario, Canada, zone 5. Anyone else with experience with either plants or seeds?