what you can do is there are some scripts that let you add vehicles. the files are a carbon copy of a DLC file/folder but is all clean for you to muck around with you can download one of those or add the meta to the already existing meta files just copy the lines over dont copy the file itself (my advice).
https://modification-universe.com/forums/index.php?/files/file/31-medic4523-dlc-download-first/
here all the needed files are in just the vehicles and XML files are needed which can be downloaded at you choice but this was uploaded for vehicles instead of putting the metas with the vehicle, it's the same principle there is a scrip i think called Modding DLC which is the same as this but is the clean starter one.
https://www.gta5-mods.com/misc/modding-dlc-pack-v
if you chose to download the latter then you should have any problems. just google/YT the rest if you cant go farther