Must be ELS. Looking fora good San Andreas State Police vehicle pack! Let me know thanks!
You can browse the #development:releases section, or look on sites like gtav mods, or lcpdfr to download cars. Look in the #development:tutorials or #server-development:server-tutorials sections for tutorials on how to convert cars into FiveM supported addons. Alternatively, you could also use the very useful forum search function, to find exactly what you need.