If you prefer not to use a mod, you can manually adjust unit counts by editing the game's .json configuration files found in the game directory. This involves locating the specific vehicle entries and changing the "count" or "availability" values to a much higher number. [EM20] Unlimited Units - Emergency 20 Compatible 1.0.0
The most reliable method is through community-created modifications. A well-known option is the , which is specifically compatible with version 1.2 and later. emergency 20 unlimited units