You can get Raid key from beating raid map, deserted city, or easier Speaker Raid. After Beating this raid you get 1 raid key, that you can use to open raid crate. You can also get raid key for robux in shop.

Units you can get from raid key:
54% - infected camera man

33% - infected large camera man

12% - disabler camera man

0.8% - engineer camera man

0.2% - Infected Titan Speaker Man ( IUTS )