In the Wisconsin area - Muntz Audio in Green Bay, RPM Speed and Custom in Sheboygan, or Radio Active sound in Fond Du Lac. I haven't seen Diamond Audio on the net either.
you dont find them online cause it voids the 1 or 3 year warranty (depending on who installs the stuff.) Go to http://www.diamondaudio.com --------> dealer lookup
TDX subs wont come out for a while...... but D5 amps are out (YES!)