Hey,47
I've noticed a number of sources offering seperate rims,hubs & spokes. I don't know how well they sell..but,I'd imagine a lot of wheels get relaced & trued,etc. Back in "the-day" I converted quite a few Honda 750s from 18" to 16" wheels (for example)and it's not all that hard. The complicated part is with the variety of wheels & hubs out there. In addition to there being inner/outer spokes, some hubs require shorter spokes on one side than the other. The trick is to sort them all out...try to keep the hub centered (side to side as well) as you're going along...and having a good balance & trueing stand. Back then, I just stuck an old R. swing arm in a vise (axle end up & leveled) and screwed a (don't laugh?) hvy duty clothes hanger wire to one side of it as a make-shift indicator/pointer...crude but effective enough. Yeah,and, balancing was (and basically still is) just a matter of finding the heavy spot in the tire/wheel (bottom when stopped) mark that spot and add weights 180* across from it until both sides were horizontally even,in the stand/swing arm.
Have'nt laced & trued & balanced a tire/wheel in decades now. But,just this Spring,I got sick & tired of paying $50** per wheel (off the bike) just for new tire mounting and balancing W/O the trueing...bought a manual tire change machine (works ok) from Harbor Freight..ordered a decent balance & trueing stand (and assort'mt of weights) thru Dennis Kirk...magnet mount dial indicator/stand on hand these days...and,now have the best balanced & retrued tires/wheels in a LONG time...knowing that my wheel bearings actually WERE repacked,and have NEW seals,too

!!