I guess legacy tech will help here. I know that a lot of businesses still run on COBOL and will probably be willing to pay well. Anyone with experience in freelancing for legacy tech ?
All this is to say, +1 for consulting/freelancing for legacy tech.
But there seems to be a lot of other companies that rely on legacy RPG. "The Four Hundred" from IT Jungle seems to be a good resource to IBM i-related information.