They are stripped and sold in separate auctions. They sell in lots, huge truckloads. The light bars often go from an older retired car to a new one. They sell huge lots of them when they switch to a new style of light bar and they take them all off. They also gradually acquire a massive pile of non-working light bars which they strip for parts.... but with LED's they don't gut the parts much now as they are virtually non-serviceable. I had been in these surplus deals before but no longer have the time for it. I did good on pallets of 2-way radios, body cams etc. We also used to get the light bars or some jurisdictions sold us cars fully equipped with dealer waivers that we would remove it all before selling or driving the cars. Those were better cars because we could properly remove things, instead of all of the damage from prisoners taking decals off with garden hoes and stuff like that. Before LED's, the light bars could be converted with amber filters and used on wreckers, construction stuff etc.
And if you would like, I can put the word out for what you are looking for. Is it the older Chicago style bar? I'll see if anybody gets back to me. Doesn't hurt to ask around, especially with texting nowadays. I'll try for you
Darn, I went too far into this. My apologies.