For example
The portal makes waybill requests for Coal , Containers and Diesel. So you send a Consist loaded with these commodities then the Portal then sends Consist back after a certain time or not at all.
Yes Dave thats what I am looking for. The actual Portal acts like an industry. Thsi could perhaps represent a far off city or port requesting comodities.
I don't know of such a portal either, but I can suggest a workaround:
Place a second portal and a "multiple industry new" offstage somewhere (behind a hill or something cunning like that). The program the first portal to spew out trains to the second, and vice-versa. Then, have your train unload/load the the MIN, before returning through the second portal.
If you wanted to control trains by hand, you'd probably need to stop the train before the first portal in an interchange siding, then hand over to the AI - set up the AI as follows: Drive to Portal1, drive to MIN, load/unload, drive to portal2, drive to trackmark interchange. Then take command of the train again.
Perhaps you could use the schedule library, to avoid having to program that every time .