Well after a long time someone asked a trick question... +5 for that :)
I don't know whether I know the answer or not, but this is the first thing comes my mind...
according to this [
^], the printer port for mainframe is
515, so try to capture the data from that port using following article
A Network Sniffer in C#[
^], if you want to parse the data from the port, then
here is the protocol description[
^]
Good luck...