I use a default Mist gtk2 theme for long time, but I was unable to find matching gtk3 theme.
So I've tried myself, and I've hacked gtk-theme-mist-redmond into https://aur.archlinux.org/packages/gtk3-theme-mist-git/.
I'm pretty happy with the result, so if anybody is interested give it a try.
PS: I use basically only one gtk3 application - spacefm, but I've tested with widget factory and even evince looks quite decent.
inactive, migrated to new user account: <mkoskar> (https://bbs.archlinux.org/profile.php?id=83604)