Our team decided to take the path of creating our own 8" mecanum wheels. here is a video of the first test run of the wheels
http://www.youtube.com/watch?v=iCDn3_rQAy8
and a picture of one of the wheels
<a href="http://s915.photobucket.com/albums/ac352/rangerrobotics3015/?action=view¤t=0130001320.jpg" target="_blank"><img src="http://i915.photobucket.com/albums/ac352/rangerrobotics3015/0130001320.jpg" border="0" alt="mecanum wheel"></a>
and one of two of the wheels in a mock base
<a href="http://s915.photobucket.com/albums/ac352/rangerrobotics3015/?action=view¤t=jhguihjk.jpg" target="_blank"><img src="http://i915.photobucket.com/albums/ac352/rangerrobotics3015/jhguihjk.jpg" border="0" alt="mecanum wheels in mock base"></a>