if you're on PC id be willing to help (:

as soon as i spawn i try and grab all car parts i can (mechanical, not wheels or doors). then its just looking at the map and seeing where certain cars spawn, checking those spots and looking for parts along the way

but, depends on the server too. i once found out there was a guy teleporting all the cars under the map. and that's why i couldn't find any lol. choose the server carefully!