Grats on your mechanochopper mastery! Bolsh can do it on Horde as well, if you're rich and interested.
The parts are sold by a goblin in K3 but only to people who have the plans for the bike learned, all for the nifty sum of 12.5K gold. Don't listen to rumors of these parts dropping off anything anywhere, they don't. Mechanical bosses in Ulduar can be salvaged for random parts such as Cobalt Bolts or the occasional Titansteel bar. I've got two Titansteel bars from Uld, but mostly you find Volatile Triggers and Cobalt Bars. Salvaging the Titansteel makes for good AH money once you get your requirement!
In addition to the 12.5K gold worth of mats you need:
• 12 Titansteel Bars
• 2 Arctic Furs
• 40 Cobalt Bolts
Bolsh is about 1/5 the way there in money and materials, I'm only half-assed going at it for the moment. *___*