Thought it would be better to type it here rather than in a Dm, so everyone can read it.
If you install WOV and VEP;
https://www.gta5-mods.com/misc/world-of-variety
https://www.gta5-mods.com/vehicles/vanillaworks-extended-pack-add-on-oiv-tuning-liveries-vanillaworks-and-other-modders
you can use them to add police vehicles that will spawn in randomly. They can also be made to spawn with LSPDFR by altering the backup file. All the vehicles can be replaced and be used with ELS. The mods are both OIV packages, so it's super easy to get them both working, but they are quite big files (~2GB), and require the mod folder to be used.