There are two ways to go about acquiring ten, or all if you're interested, vehicle parts in the game.
The first method is through the in-game and on-map 'Hijack Targets' that Ellie will hint are near you as you're exploring the map. IGN has an interactive guide for this and there's roughly enough for this if you wait it out.https://www.ign.com/wikis/borderlands-3/Hijack_Target_Car_Pa...
The better method would be trying to hijack enemy vehicles manually. Some of the better car customization pieces and upgrades can come from this. Simply walk up and hold 'X' to hijack. "Gamewith.net" has a good guide that includes every part in the game. https://gamewith.net/borderlands-3/article/show/11068
If you needed a video as a visual guide, YouTuber "Syke" has you covered here.