Thanks for the pointer! Do you (or your friend) happen to have a link to a sample job post that I may be able to use to identify these opportunities in the future?
Unfortunately I don't have any link to such a job post, but when I've seen them in the past they've clearly stated what they are about, so keywords like "COBOL" or "Mainframe" would certainly find them. Sorry I couldn't be any more help.
https://www.ibm.com/it-infrastructure/z/education/zxplore