For unloading, yes there are converyor devices used to unload semi's and such which you can get at industrail supply places.
For loading.. I have seen powered belt conveyors (Same source)
In both cases.. I question the value
What I did....
I added a toggle either in parallel or series (Depending on the age of your step controller) with the door switch.
Flip the switch and the controller thinks the door is closed and retracts the steps.
now one person inside and one outside, you can quickly and easily pass goods from outside to floor of coach, and from there to where it goes (I add a small step to make it easier for the inside person)
Or the reverse if unloading.