Sounds like a local PD here that replaced all their Remington 870's with Mossberg 590's because the 870's were "worn out". An insider told me that they had an inlfux of Marines and they wanted to use the same shotguns they'd used in the Corps.

State or scarfed up by outside companies?

I don't think a police force can obtain enough ammo to wear out a Glock in four years. I personally know of one that a friend had a hand in testing with over 140,000 rounds of 9mm before they gave up trying to wear it out.