It's only money and the only way to find the body you want.
I have personally purchased a model kit just for the wheels and tires before.
Sometime later I usually find a use for the rest of the kit because I throw nothing away because seats, engines, bodies, decals and custom parts can find there way into other projects.
I still have boxes of tires, wheels, Motors and other misc parts left over from my static modelling days as a kid. I have several static cars I'll likely never finish that are decent candidates for slotting. My GF picked out the AMT 1953 Corvette for her car. that static kit is at least 20 years old, probably 25. I've got a couple first gen dodge viper roadsters, a Viper GTS coupe, A miata, a Monogram maserati 3500GT, and a bunch of cars I built but that have been broken or fallen apart over the years. there's a1960 corvette that I built, but the body came apart from the chassis. last week I spent some time re-gluing its trim for eventual resurrection as a slot car.
@GatorBob, Hermit, I completely spaced out about looking at that tube of Lenk solder I've been using. I'll try to remember tonight, if my apprent cognitive decline doesn't worsen ;-/
@ Jariius, BTW that Rat Pickup with the flattie is pretty farking sweet.