I don't know of any. I don't consult for the mainframe systems themselves. Usually I get pulled in when the client realizes that their last mainframe developers are years away from retirement, and they cannot find any new mainframe developers to hire. That starts a mad dash to migrate/replace the mainframe solution without disrupting the entire business. Despite the existing codebase, these projects are very difficult because noone knows how they work anymore.

At one of my clients they had one mainframe developer left that knew their systems. She had already tried to retire, but they got her to agree to stay on for 5 years in return for bags filled with money. That meant they had 5 years to rewrite on a platform they could actually hire people for. 5 years to replace a system with decades of history.