Well, unfortunately there isn't anymore. There used to be a couple of boards dedicated to the hacks, but InfoPop (makers of this UBB software) decided to actively go after those users manipulating the UBB code, so the hacks boards pretty much went south.
http://www.ubbdev.com/ubbcgi/ultimatebb.cgi
The above site used to be THE SITE for hacks, but they don't offer freeware hacks anymore. Although, if you scrounge around in the database, you can run across people who still "fiddle" with the freeware boards, and may have some hacks posted. Good luck!