Slitherine

There are several scenarios (especially mp ones), on which my side hasn't got available Air transports, thus rendering my parachuters useless.

Would you please implement a feature so that we can buy additional Air transports?

IIRC you can load them into a air transport on any airfield - just like any other infantry unit. This feature should probably have a tutorial popup.

Also, you can move them to a city. Buy a truck. Then move to airfield. Then embark, disband truck.

you can now fly over and over again. You traded your truck for an airplane transport.

You cannot move them with air transport if scenario doesn't have air transport availability defined. For some scenes such feature is intentional.