I'm running a fairly fresh arch install.
pacman -S gnash-gtk but this doesn't work
How do I get midori or any other browser to play flash videos (youtube, Iplayer, etc)
You can then install the package from the AUR like this:
yaourt -S midori-flash
I've not checked to see if the package is available for arm, but if it is not then you will have to follow these slightly more complicated instructions on building from the AUR.