Finding Bicycle Parts How would I find bicycle parts cross-referencing make and model? I own a Dept. Store Schwinn Dual Sport (GTX), and before I begin dismantling the bottom bracket for servicing, (it's been 3 years since I bought this bike brand new with a lot of exercise mileage); I would like to have the parts in hand. I've searched and Googled ad nauseam and I find nothing. Also, I can't find a parts blowup specific to my make and model, (just the generic drawings in the so-called Schwinn User Manual....which is probably used for other models). Why is it so hard to find this information? What purchasing source do the bike shops use?
Generally, parts are somewhat standardized. For example, bottom brackets only come in a few types and different size. 

Given its a recent department store bike, you likely have a standard square taper bottom bracket with ISO threading. You can take the relevant measurements (spindle length, shell width, etc.), but the easiest way for bottom brackets is either read them off the existing bottom bracket (usually labeled) or take it to a bike shop so they can measure it quickly and give you a new one. 

As for other parts, you can usually identify them by what family of parts they belong to if they're in the drivetrain (# of speeds and manufacturer), or measure them for things like seatposts or handlebars (which are also standardized, e.g. road bikes use some sizes, mountain others).