Do you mean police vehicle slots? If so
LSPD
police
police2
police3
police4 (unmarked)
policet
riot
LSSD/BCSO
sheriff
sheriff2
SAHP
policeb
police4 (unmarked)
North Yankton
policeold1
policeold2
Park Ranger
pranger
Lifeguard
lguard
I'm missing some, such as the military, and there might be others that I'm forgetting. Bare in mind, due to the limited slots for some of these, and due to SAHP not even having a proper marked unit, people - myself included - just use addon vehicles so we can expand and have proper fleets.