Since my messages for increasing the amount of central stations were deleted, I will propose a different approach.
What if you were able to purchase an extension onto the regular fire stations that would allow that particular station to be transformed into a main fire station?
The main fire station would allow it to be equipped with all the abilities of a central fire station minus the ability to create alliances.
Cost of the extension would be $150,000 and would take 12 hours to build.