I can agree with you on the spare. But seriously, if you can't find 255/40/19's, you suck at the interwebs. Bridgestone, Continental, Michelin, Hankook, Goodyear, Nitto... Take your pick, they are everywhere. You can even get the Michelin pilot super sports (arguably the best street tire ever) in 255/40/19.
Just goto tirebuyer.com or tirerack.com and search for 255/40/19 then spend your money.
Black 2013 GT Premium | Track Package | Recaros | GT500's | JBA H-Pipe | Borla Over-Axles | OEM GT500 Spoiler | Koni Yellows | Steeda CAI/Tune | Steeda Ultralite Springs | Steeda Adjustable UCA/PHB | Steeda Billet LCAs | MGW | Forgestar F14's