Yes- you can change to a hollow axle. The new axle will need to be shorter (i.e., not extend significantly past the dropout.)
Yes- axles are available. See a bike shop that has lots of old parts. Take the existing axle. Take an existing nut or cone.
No- vintage axles such as yours are not typically hub specific. Get the correct length, threading, diameter and you are good to go. Get a QR skewer that fits the length axle you need.