Is there any way to get Adobe Flash on Haiku?
No you may as well consider flash dead. Even Adobe is abandoning it for HTML5 which haiku is slowly gaining support for.
There was a Gnash port that worked in Bezilla however support for the Bezilla plugin was dropped and Gnash now only runs as a desktop app if you can get it to run at all. It might be updated once haiku reaches beta or R1 I bet though to and Web+ might add support for it who knows.
There is GNASH but it needs an update:
http://haikuware.com/directory/view-details/multimedia/video/playback/gnash-087