We have most platforms from IBM, z (Mainframe), iSeries (AS/400), p (AIX), plus about everything windows.
Moving off core systems (z/i/p) isn't simple mostly because of the amount of data combined with all the custom applications. every attempt to move the apps off the z don't come to fruition because of scope and the fact it just works. the i is increasing its load to pick up from the z and getting a good dose of webfacing and rest services. these are dead simple to implement and many reuse all the existing code.
talent wise, it really hasn't been much of a challenge in Atlanta/Dallas to find those who can support what is needed. the language isn't the biggest road block for many mainframe systems, its the file systems that can trip people. the i is pure DB2 so anyone versed in SQL can use it and RPG looks more like Pascal these days than that three column stuff people normally associate with it.
the one thing many here don't understand is just how many companies are invested in mainframe, i, and large p series systems. don't scoff at these platforms. with modern tools they can be webfaced just fine and the advantage their default coding languages have is they are business math oriented and simple. with modern features and file systems it just comes down to, what is management comfortable with and does it serve the companies needs.