Stiffy,
I have HTR Z 315/35/17 Sumitomo's (rear) and HTRZ II 255/45/17 (front) fitted to knock-off Vintage rims ready to put onto my build when its finally finished.
I purchased them on 7/8/07 over the Internet from 'The Tire Rack' in Indiana USA. After sending them the wire transfer, it only took 6 days before they were on my door step. The best part was the price: The 315's were $US96 each and the 235's were $US92 each. On top of that, I paid $US191.84 to freight the four tyres from USA to Sydney with Fed Economy.
The four tyres and freight came to $A710.05 (THATS AUSSIE DOLLARS)
Your contact at Tire Rack is Fred Helmuth. I found him extremely easy to deal with.
His email address is:-
fred@tirerack.com
Good luck,
Baz.