In my workplace, there are a few options: When a disabled person is on a certain floor above ground floor, there will be a special chair they can be put in, that allows one person to maneuver them down the fire escape. Multiple people in the company are trained on the use of this contraption and are notified before the evacuation is necessary.
When there are more wheelchair bound people in the building than there are evacuation chairs available, they'll have to be taken to the fire escape behind double fireproof doors, where the area is pressurized with clean air. There the firemen will evacuate them.
A third option is the area where the elevators are. It closes automatically and has a fireproof door where you can wait in front of the elevators for the firemen to evacuate you using the elevators (or otherwise).
Normally there aren't that many wheelchair bound people in the building that need those chairs, because visitors are normally confined to the ground floor. On a floor where a disabled person used to work (now retired), one of those chairs was permanently available.
Edit: the ones we have resemble these https://evac-chair.com/
Take a chainsaw with you next time. If they complain that you don't have a motor, offer to demonstrate to them that you do in fact have one (without being threatening of course).