Around Dallas I see the FBI Crown Vics with either an am/fm disguise antenna or a single UHF antenna. They don't have much need for multiple radios. However, you will see the Secret Service with multiple radios and antennae, especially in presidential protection details, and they are almost always black. You'll see Border Patrol with multiple antennae too, although I don't think they run too many unmarked vehicles.
I've also seen Army Corps Of Engineers cars and trucks with two or three antennae on them. Although their radios are VHF, their LE personnel are sometimes dispatched by GSA police, who are on UHF. And around here, they need 800 for interops with local agencies.